|Dates||2011 (vessel could not handle holding the Leviathans)|
|Occupation||Vessel for Leviathans|
|Episode(s)|| 7.01 Meet the New Boss|
7.02 Hello, Cruel World
Too late! Cas is umm... He's gone! He's dead! We run the show now.
– Leviathan!Castiel, 7.01 Meet the New Boss
Castiel opens a door to Purgatory and absorbs all the souls residing there, unknowingly absorbing the Leviathans as well. He then uses this power to obliterate the archangel Raphael and declares himself a new and "better God."
- "Oh, this is going to be so much fun."
After killing all of Raphael's loyalists in Heaven, Castiel proceeds to perform many miracles and selfless deeds in his efforts to bring peace and order back to the world. Eventually, the Leviathans begin to stir within Castiel and demand to be let out. Castiel refuses to acknowledge them, however, and continues his campaign of righteousness. The Leviathans take their toll by eroding Castiel's vessel, causing him to black out and gaining control of his vessel for a brief moment.
When Castiel comes to his senses, he realizes the carnage the Leviathans have wrought and seeks out Sam and Dean's help in returning the souls to Purgatory. This is only partially successful, however, as the Leviathans succeed in "holding on" inside Castiel and soon after take full control of his vessel, declaring him dead and gleefully attacking Dean and Bobby.
- "We'll be back for you."
Before the Leviathans can finish Dean and Bobby, Castiel's vessel begins to rapidly deteriorate and oozes black blood. Knowing it cannot contain them all for long, the Leviathans abandon Dean and Bobby with the promise to return and directs the vessel to a nearby water supply. They then submerge the vessel and it implodes, releasing countless Leviathans. Castiel and his vessel are gone, leaving only his tattered trench coat behind, which Dean retrieves.
The Leviathan Chet reveals that as a result of all the Leviathans possessing Castiel, they have absorbed all of his collective knowledge, giving them an advantage in tracking the Winchesters through their aliases.
It was revealed that after the Leviathans released themselves into the water supply, Castiel was revived by God without his memories. He becomes a faith healer in Colorado known as Emmanuel Allen; husband of Daphne Allen. After Dean and Meg take him to Northern Indiana State Hospital to save Sam from his psychosis, where he smites a group of demons, he regains his memories, including when he returned the souls to Purgatory.
While the Leviathan leader Dick Roman talks with the other Leviathans in the conference room at SucroCorp headquarters, he remarks that the last time they were all together, "we were inside that angel."
Meg and Crowley reveal that as a result of all the Leviathans possessing him, the resurrected Castiel possesses the ability to tell the them apart no matter what form they take. This proves to be the key to killing Dick Roman and putting a stop to the Leviathans' plans. Before dying, Dick thanked Castiel for "the ride into paradise."