There are things much older than souls in Purgatory. Long before God created Angels and man he made the first beasts: the Leviathans. I personally found them entertaining but he was concerned they'd chomp the entire Petri dish. So he locked them away. Why do you think he created Purgatory? To keep those clever, poisonous things out.
|Powers and Abilities||Super strength, Regeneration.|
|Vulnerabilities||Borax, Beheading can slow them down and Powerful spells can temporary incapacitate them.|
|Appearance||Black goo, or human with giant teeth and bifurcated tongue|
|Episode(s)|| 7.01 Meet The New Boss|
7.02 Hello, Cruel World
7.03 The Girl Next Door
7.05 Shut Up, Dr. Phil
7.06 Slash Fiction
7.09 How to Win Friends And Influence Monsters
7.10 Death's Door
7.11 Adventures In Babysitting
7.12 Time After Time
7.16 Out With The Old
Leviathans, also called the Old Ones, pre-date the creation of humans and angels, as well as the soul itself. They would also pre-date any beings with souls, such as monsters. They are therefore among the first creations of God.
Death describes them as immensely powerful and hungry. Before God went on to create more creatures, however, He felt that the Leviathans threatened to consume and destroy everything 'in God's petri dish'. For this reason, Death states that God created Purgatory and sealed the Leviathans inside to contain them and their hunger.
When Castiel opened the door to Purgatory quite recently and took in the power of the souls stored there (to increase his own angelic power), he also took in the Leviathans. With the help of Sam, Dean and Bobby, Castiel finally expels the souls back to Purgatory, but some of the Leviathans "held on". Castiel's Vessel is taken over by the Leviathans, and claim that Castiel is dead and no longer in control. They manage to guide Castiel's vessel into a nearby water catchment just before the vessel disappears in a whirlpool, releasing them into the water supply.
The number of Leviathans that escaped from Purgatory is unknown. The Leviathans operate within a hierarchy lead by Dick Roman. Their 'modus operandi' is to take on the forms of humans who have valuable skills, or are in positions that may be useful, particularly positions of power including the military and corporations. Their ultimate goal is not yet known, but they appear to be playing a long game, infiltrating human society and keen not to draw attention to themselves. Dick Roman says their golden rule is "there's no such thing as monsters".
They are hunting down the Winchesters, as they perceive them as a threat.
The Leviathans have sharp teeth within an expanding jaw, and possess a bifurcated tongue. They feed on human internal organs - sometimes with cheese.
They can mimic a particular human being following contact with one, or if they obtain DNA from a person. They are then aware of all that person's thoughts and feelings, and even hallucinations. All the Leviathans now outside Purgatory absorbed everything that Castiel knew, as he was their original vessel. When wounded they "bleed" black goo.
'Bibbing' was first mentioned by Dick Roman when he told Valente: "Next time, call me with a win. For your sake. Please don't make me bib you." When Dick decides that Dr. Gaines's experiments are drawing too much media attention, he decides to bib him. This involves literally placing a bib on him, and then Dr. Gaines eats himself until nothing is left - except a goo stained bib. So far this is the only known method of eradicating a single Leviathan for good.
Sam and Dean refer to them as 'big mouths'.
Powers and Abilities
- Possession: Leviathans can possess any human they come into contact with in their fluid form. This person becomes their physical embodiment of sorts. These shells bleed black ectoplasmic blood when injured and can reshape their jaws to display long sharp teeth and a two-pronged tongue.
- Shapeshifting: Once a vessel is taken they can reshape it into any human form they touch. They require only a fragment of DNA to transform into a person; even lost hair will do. The creature possessing a little girl takes the form of a doctor by touching his arm. They can also absorb the memories of anyone whose form they take, much like a Shapeshifter, but without requiring the person to remain alive.
- Super Strength: They are shown to possess greatly enhanced strength; at their first meeting, they are able to hurl Dean and Bobby across a room with little effort.
- Healing/Endurance: Leviathans are extremely resilient, surviving multiple shotgun blasts with silver shot, including one to the head at point blank range. One also survived and reassembled itself after being crushed by a falling car. They can even re-attach their heads if decapitated. 
- Borax: Leviathans are highly susceptible to materials that contain the chemical compound Borax (Sodium Borate) such as household cleaning products. Contact with their skin results in an instant burning effect that can reduce them to charcoal-like husks if they are exposed to too much. It is suggested that they will eventually heal from the effects, however. Their leader, Dick Roman, may be less susceptible to the chemical.
- Beheading: Removing a Leviathan's head disables them temporarily. But unless the head is kept far away from the body it will re-attach itself. The combination of burning them with Borax and then beheading them and separating the head and the body appears to be the only way to put them down indefinitely, assuming the head has no way of finding its way back to the body.
- Witchcraft: Leviathans show susceptibility to witchcraft. It can incapacitate them temporarily.
Leviathans on The Loose
The first leviathan appearance is when they take over Castiel. As Leviathans take the form of humans, they are referred to here by their human names.
- Leviathan Boss - Dick Roman
- Annie, who later becomes Dr Gaines.
- Two Members of the Stockville Sharks Swim Team, who later become a Head Nurse and a Hospital Administrator at Sioux Falls General.
- Valente - The FBI Leviathan
- Leviathan!Sam and Leviathan!Dean
- Susan - Dick's Assistant
- Joyce Bicklebee
Whilst ingesting all the souls from Purgatory to became the new God, Castiel also took in the Leviathans. The Leviathans struggled for control, briefly taking control of Castiel's Vessel to smite people that even the now-wrathful Castiel didn't intend to, and causing his vessel to physically deteriorate and potentially explode.
With the assistance of Dean, Sam and Bobby, Castiel returns the souls to Purgatory. But "some" of the Leviathans hold on, and assume control of Castiel's vessel. Stating that Castiel is dead, the Leviathan!Castiel attacks Dean and Bobby with manic delight, remarking: "Oh this is going to be so much fun."
After having revealed themselves to Dean and Bobby, the leviathans quickly realise they cannot remain inside Castiel's vessel as it begins to rapidly burn up and are forced to leave for the time being; they promise to return and finish what they started. Leviathan!Castiel staggers out into the open and submerge themselves in a nearby municipal water source, abandoning the vessel, leaving only Castiel's bloody trenchcoat behind.
The Leviathans then disperse to take separate vessels of their own by various means of exposure to the tainted water. One takes a girl whilst she drank from a public water fountain, for example. Two of the creatures infect a pair of gym students and use them to kill and devour two other students, leading Dean to their whereabouts. The creature possessing the girl meets with another Leviathan - Edgar - to discuss their next move and the "boss" they take their orders from.
The girl comes up with a plan to solve their feeding problem and steals the form of a doctor - Dr Gaines - at Sioux Falls Hospital. It then uses the position to acquire easy meals. Its act of cannibalism is witnessed by Sheriff Jodie Mills, who escapes the hospital with Bobby's help. Edgar arrives with the two gym student Leviathans, which take on the forms of members of staff. Bobby investigates one of the bodies and is confronted by the Leviathan Dr Gaines, who recognises him from before, when it was inside Castiel.
Bobby subsequently escapes the confrontation and races back home, informing the boys of his discoveries along the way. When they return to his house they discover it burned down and Bobby missing, however. Sam and Dean are then attacked by Edgar the Leviathan who informs them that they are considered "competent" enough that the head Leviathan wants them dead. The boys succeed in defeating it by dropping a car on it. Both suffer severe injuries, however, forcing Dean to call for an ambulance.
Back at Bobby's, the black blood of the Leviathan Edgar, spills back into the body and its hand twitches as a sign of life.
Bobby arrives at the hospital where Dr Gaines works to rescue Sam and Dean. He tells Dean to meet him in the ambulance bay and tosses him a pair of crutches, then grabs the gurney holding an unconscious Sam. He stows Sam in the back of the ambulance and climbs in the driver's seat. Dr Gaines receives a call telling him the Winchesters are in the hospital, and with the Leviathan nurse he goes in search of the brothers. They spot the ambulance and toward it. Dean board the ambulance just in time and all escape.
Three weeks later, Bobby's contacts tell him that the leviathans at the hospital - Dr Gaines, the head nurse and an administrator - have disappeared. He says that other hunters are reporting similar attacks and that "they're like shapeshifters only a lot more into eating folk. And nothing can kill 'em."
A Leviathan has taken the form of an employee working for a credit card company called Chet, and has set up flags on credit cards with the Winchester brothers' known aliases. One is triggered when Sam uses the pseudonym Lemmy Kilmister in Whitefish Montana. Chet calls Edgar for guidance, and Edgar tells him to get after the brothers. He tracks down the location where the card was used, and finds Sam on the security footage. He calls Edgar again to tell him that he is on their trail, then pours a vat of hot cheese on the bound and gagged store clerk, and eats him.
Chet gets instructions by phone as to the Winchesters' location and says he's about a day and a half drive from Prosperity, Indiana. When he finds Sam and Dean, Dean shoots him, but his body simply pushes the bullet out. As Chet is about to attack, Don Stark enters and paralyzes him with some sort of spell, which he says will disable him for a day or two. He advises the Winchesters to put the creature in a bottomless hole.
Sam and Dean bind Chet with chains, and put him in the back of the Impala.
Chet is chained to a chair in the basement of Bobby's cabin, still weakened by Don Stark's spell. Bobby tries every method in the book to find a means to harm the Leviathan, but everything fails, much to Chet's amusement. Whilst preparing electric shock, Bobby brushes against Chet's arm, allowing him to take his form in order to mock him on a personal level. Bobby loses his cool and cuts Chet's head off, which seems to be the solution he was looking for.
Bobby later finds Chet re-attaching his head, however, and wonders how else he might harm the monster when something starts to drip through the ceiling and onto Chet, who screams in agony as the liquid burns through his skin. Bobby rushes upstairs to find his guest, Sheriff Jodie Mills, cleaning the floor with Borax products. He quickly douses Chet with the stuff and beheads him once again, this time keeping his head in a cardboard box and instructing Jodie to take it far away and "drop it in the drink".
Meanwhile, two more Leviathans have taken Sam and Dean's form and are going on a rampage from town to town, killing people en masse. This causes the authorities to place Sam and Dean on the top most wanted list and a manhunt begins, with two FBI agents taking a particular interest. The doppelgangers succeed in luring them into a trap and Sam and Dean are arrested by the police.
The Leviathans then infiltrate the police station and try to kill the Winchesters, but are caught by surprise when Dean uses Borax against them and decapitates them as informed by Bobby. With their heads missing, one of the FBI agents, actually a Leviathan, informs his "superior" of the situation and is advised to adopt new tactics in hunting the brothers.
Elsewhere, the Leviathan superior, Dick, enters his limo and is greeted by the demon Crowley, who proposes an alliance between their two factions. Dick coldly refuses his offer, however, considering Crowley a "hideous mutation" and not worthy of his attention. Crowley leaves, insisting the Leviathan keep his offering of infant-flesh muffins.
Sam, Dean, and Bobby follow a suspicious meat truck from a Biggerson's Restaurant to a building run by Dr Gaines. Their first clue that something is very wrong is the arrival of Edgar, who is meeting with Dr Gaines. Dr. Gaines has been experimenting on food to create an addictive product that will pacify and fatten humans for ease of Leviathan consumption. He is behind the new Turducken Slammer at Biggerson's. However, a small percentage of test subjects have a had a bizarre reaction involving massively enlarged adrenal glands that drive them into a zombie-like, cannibalistic frenzy. Their behavior has led to newspaper reports speculating about the Jersey Devil. Edgar warns Dr. Gaines to burn his failed subjects because their leader, Dick Roman, is coming to check on him.
Dick arrives, and Dr. Gaines shows off his lab, in which test subjects are passively watching surgery on television next to a dead relative. Dick likes what he sees, but reminds Dr. Gaines that his work made the papers. Dick wants to make this a "teachable moment" for his other subordinates. His assistant, Susan, places a bib around Gaines's neck, and he reluctantly eats himself alive.
The Leviathans capture Bobby, who has been spying on them, and take him to Dick's office. Dick tells Bobby that he is going to eat him, but he is mildly impressed by humanity's achievements, including the gun. He speculates that Sam and Dean will soon attempt to rescue Bobby, who tries to convince him otherwise. Dick is proved correct when Sam and Dean burst into the facility with spray bottles of borax and start spraying the Leviathans. Dick commands Bobby to remain in his office and leaves to take on the brothers, taking a gun with him. Bobby runs to the desk, finds folders of information on Leviathan plans, and grabs one of Dick's fancy weapons. Susan tries to stop him, but Bobby shoots her in the head, buying enough time to get past her.
Sam and Dean try their borax on Dick, and while he burns, he seems less susceptible to damage. The brothers by enough time to get outside the building and start their van. Bobby runs after them and dives inside just as Dick comes out of the building, shooting. He hits Bobby as the van speeds away.
Dean finds Dick in his car outside the hospital where Bobby is fighting for his life. When Dean yells that Dick Roman is there, passers-by start taking pictures with their phones. Dean challenges him to kill him there, but also points out that - being famous - he can't kill him without bringing attention to the Leviathans. Dick laughs, seemingly unconcerned by Dean's threats.
Dean has given Frank the numbers 48495 which Bobby wrote on Sam's hand before he died, and also asked him to research Dick Roman. Having not heard from him for a month, Dean returns to Frank's house to find it deserted. Frank confronts him, and they both have to shed some blood to prove to the other they are not a leviathan.
Frank has moved all his equipment into an R.V., after feeling he was being watched after he started investigating Dick Roman. Frank says he has found evidence of the leviathans in posions of influence. He tells Dean he has found nothing on Bobby's numbers, but then he tried combinations with adding a sixth number and realized they are coordinates to a field in Wisconsin, owned by Dick Roman.
Frank and Dean travel to the area and disguise themselves as phone company workers. They discover surveillance covering the area and retreat to Frank's RV to monitor it. They discover Amanda Willer, who works for Roman Enterprises, surveying the site for construction. It is unknown if Amanda is a leviathan.
Before he dies, Chronos the God of Time, tells Dean and Sam, "You want to know your future? I know your future. It's covered in thick black ooze. It's everywhere. They're everywhere. Enjoy oblivion."
Frank reports to Dean that Leviathans have infiltrated the luxury cruise ship industry.
Dean continues to insist Frank research the Leviathans and try and find out what Dick Roman is planning. Frank reports to Dean, Dick's funding an archaeological dig, a factory in Saudi Arabia, and a fishery in Jakarta. He thinks they are behind the new Biggerson's restaurant in Butte, Montana. Frank tells dean Tromso in Norway has "zero leviathan activity".
While investigating cursed objects in Portland Oregon, Dean and Sam discover that leviathan realtor Joyce Bicklebee and her assistant George, are acquiring properties from local owners, and killing those who refuse to sell. After george helps the Winchesters kill Joyce, he reveals that the Leviathans are planning on building a research facility, in order to find a cure for cancer. When Sam asks why, George replies: "'Cause we're only here to help."
Leviathans in Lore
- In the Judeo-Christian tradition a Leviathan is a giant sea monster, described in the Book of Job Source
- The Talmud Baba Batra 75b states that the archangels Michael and Gabriel will be the ones who slay the Leviathan. Other legends say God will slay the beast. Source: Leviathan in Judaism
- Death also refers to the Leviathans as "The Old Ones" a term used by H.P. Lovecraft in the Cthulhu mythos to describe ancient powerful alien beings who come to Earth. A race called the Old Ones also features in Stephen King's Dark Tower Series.
- In Binsfeld's Classification of Demons, Leviathan is the name of Envy, one of the Seven Deadly Sins
- Sera Gamble and Bob Singer talk about Leviathans with AOLTV