McNair was a hardworking man until he was kidnapped by Herrick and the vampires who put him in a cage with a werewolf. McNair won the fight with the creature but he was infected with lycanthropy. One night he had killed two people, the biological parents of Tom McNair and he managed to infect the boy with lycanthropy, feeling guilty, he took the boy in and raised him as his own.
George and Nina met him after meeting Tom while looking for advice about Nina's pregnancy. Tom and McNair, eventually, go to Hononlulu Heights to help. They became good friends.
McNair got a gash in his leg, so he went to Hononlulu Heights to get medical help from Nina. He realised that Herrick was living there and he started planning his revenge. (Source)