Isaac Lahey was a student at Beacon Hills High School who was also on the lacrosse team and a member of both Derek and Scott's packs.
He is played by Daniel Sharman.
Isaac lived with his father, Coach Lahey. His brother, Camden, was killed in combat in while serving in the US military. Isaac's father was abusive, locking his son in an unplugged chest freezer in the basement for long stretches. The abuse led to Isaac developing claustrophobia.
Mr. Lahey ran the Beacon Hills Cemetery where Isaac also worked. After being trapped in grave by an overturned backhoe, Derek Hale rescued Isaac.
After a fight with his father the next night, Isaac sought out Derek and received the bite, becoming a werewolf.
After the death of his father at the hands of the Kanima, Isaac moved in with Derek.
Unlike the other pack members, Isaac would question Derek's choices and motives as a leader. Their relationship became strained after The Alpha Pack attempted to get Derek to kill the remaining members of his pack, including Isaac. In a misguided attempt to keep him safe - Derek threw Isaac out of his loft. Homeless, Isaac moved in with Scott McCall and his mother.
While attempting to defeat the Alpha Pack, Isaac began to develop an attraction to Allison Argent. Their relationship advanced in fits and starts, culminating in a single night together.
- “Well, I'm a little bummed about being a fugitive but other than that I'm great.” — Isaac to Scott in Ice Pick.
- “You could've blinded me.” — Isaac to his father in Shape Shifted.
- “Nah, I was thinking I would channeling it into killing her. I'm not very good at writing.” — Isaac to Stiles about killing Lydia in Venomous.
- “I came to win.” — Isaac to Scott in Battlefield.
- “How come you get his shirt and I get a shoe?” — Isaac to Scott about finding Stiles in Master Plan.
- “How do you two losers even survive?” — Isaac to Scott and Stiles in Raving.
- “So, what are you? Some kind of witch?” — Isaac to Dr. Deaton in Raving.