Alpha
An Alpha is the progenitor of a line of supernatural beings, aka "the original monster". However, they do have mothers as the Alpha Vampire remarks, meaning that it was perhaps a combination of lineages from different parents that created Alphas.
According to lore they have a connection with all their 'offspring', which allows the Alpha to locate them.6.02 Two And A Half Men For at least some Alphas, the connection also allows communication through shared visions or telepathy.
List of Alphas
Alpha Shapeshifter
First appearing in 6.02 Two And A Half Men, this shapeshifter has gathered a following of its 'offspring' and is apparently generating more shapeshifter children by posing as human husbands and impregnating their wives. When Sam and Dean rescue one of its children, the Alpha Shapeshifter storms the Campbells' compound and kills Mark Campbell, overcoming several gunshot wounds and tranquilizer darts, as well as a silver knife to the heart. It then reclaims the baby from Dean and leaves. This shapeshifter is able to transform in just a few seconds without shedding its skin.
Alpha Vampire
The Alpha Vampire is first glimpsed in 6.05 Live Free or Twihard, briefly flashing in the minds of its "children" as it commands them to recruit more for its army. Nothing is known about this particular monster, aside from the fact its "messages" can be heard by all vampires and render them unconscious.
In 6.07 Family Matters, Samuel and his people capture the Alpha Vampire and attempt to interrogate him, but he is extremely resistant to pain and doesn't give Samuel any information. After Samuel leaves the room where he is being held, he is approached by Dean and Sam and he reveals to them that, though he is the first vampire, he has a mother. He also tells them that Samuel is torturing him for information about Purgatory which is where the souls of supernatural creatures go, and where it is located.
Shortly after their conversation, he escapes his cage and almost escapes, but demons appear and take him away on Crowley's orders. It is revealed that Samuel has been working for Crowley, who will to continue to question the Alpha Vampire about the location of Purgatory.
Alpha Skinwalker
The Alpha Skinwalker is first seen in 6.08 All Dogs Go To Heaven. This Skinwalker starts recruiting other skinwalkers to further 'his cause', which will start when he gives 'the signal' to his skinwalker soldiers.
