Castiel was a member of Camp Chitaqua, serving under its leader Dean Winchester. He is the alternative reality version of Seraphim Castiel.
Background
History
Castiel likely rescued Dean from Hell and watched over him per Heaven's orders. He broke his ties with Heaven after Dean exposed them as wanting The Apocalypse to happen. Despite his newfound loyalty towards Dean, Sam Winchester ended up saying "Yes" to Lucifer and victory fell towards the Archangel rapidly.
The Croatoan Virus was unleashed and millions of humans died. Instead of fighting against Lucifer and his demonic army, Heaven abandoned Earth either by choice or by force. Castiel, without his connection to Heaven, gradually lost his powers over the course of five years. He remained loyalty to Dean despite the situation, and became a member of Camp Chitaqua.
Season 5
In 2014, Castiel met a time traveled Dean Winchester and was able to deduce that Zachariah was responsible. He was met with repulsion and concern from Past!Dean over his new lifestyle, though Castiel wasn't ashamed that he had become attached to drugs and women.
When Dean met his counterpart, he was offered a chance to partake in a final mission against Lucifer. Having obtained The Colt, 2014!Dean was determined to confront Lucifer once and for all. Despite knowing it was a suicide mission and he and the other members were to act as a decoy, Castiel obeyed the command to join the mission.
At Detroit, 2014!Dean confronted Lucifer while Castiel and the others fired guns as demons and infected people. Past!Dean saw and heard the firing momentarily, leaving Castiel's actual fate unknown.
Powers and Abilities
Supernatural Awareness - Although Castiel had been stripped of most of his powers, he was still able to detect that Past!Dean had time traveled to the future.
Personality
This Castiel had become bitter and depressed with the state of the world and humanity's losing battle against the demons. Most of all, he was unhappy and unable to do anything about his Dean's change in behavior. His former ward had also become bitter but also ruthless, willing to torture others, kill the slightly infected, and sacrifice his own men, even Castiel himself.
Being the only angel left to fight alongside humanity also took a toll, though Castiel brushed it off by focusing on women and drugs during his free time. He enjoyed arranging orgies and caring little on his hygiene. Stripped from most of his powers, Castiel had to rely on human weaponry such as guns.
Much like his own counterpart, Castiel retained a strong loyalty towards Dean. He chose to go on a suicide mission on Dean's command. Although he had accepted his fate, he openly preferred Past!Dean, showing a longing for a world prior to his own.