Aidan was a hunter whose family was killed by a vampire. He was taken in by Victor Rogers along with Krissy and Josephine, who also suffered similar fates.
Season 8
He and Krissy pretend to be a couple and hole up in a car at a local make-out spot. As planned, a vampire stalked them. Krissy pretends to be scared and while it was distracted by her, Aidan decapitated it from behind. He claimed that the vampire was the one that killed his family. They were unfortunately caught on camera. They were saved by Sam and Dean who recognised Krissy and managed to keep the police off them.
While laying a plan to ambush Josephine's vampire, Jimmy Day, Aidan flirted with Krissy. But she shot him down saying she had a boyfriend with whom she Skypes. Aidan and Josephine cautiously stalk towards Jimmy Day's room, while Krissy kept an eye on them through cameras. Sam and Dean eventually caught up with Krissy. Jimmy escaped from his room before Aidan and Josephine could kill him. Krissy rushed to the spot and weakened Jimmy by using dead man's blood. Jimmy protested his innocence, but was killed by Josephine.
Later, when on the hunt for Krissy's vampire, they encountered Dean already at the spot. Dean managed to calm them down by showing that the monster they were hunting, was newly turned. They headed back to Victor's to question him. There they found Sam bound and about to be killed. Victor admitted that he had their families killed by Seth. Seth then took Aidan hostage to ensure his safety. But Krissy took him down by shooting darts filled with Dead Man's Blood.
He later helped the newly turned vampire to be cured and Dean warned him not to break Krissy's heart or she'd kill him.