Sam and Dean first met Glen as he was leaving Madison's house. Madison told them that Glen was very nice and friendly. They later found out that Glen was the one to bite her, however, causing her to become a werewolf. Like Madison, Glen was not aware of his other half and was acting solely on his instincts. While going after a prostitute, Glen was confronted by Dean who shot Glen three times in the chest with silver bullets. Mortally wounded, Glen's human personality reemerged and he begged for help, terrified by what had happened and his lack of knowledge of how he'd gotten there. Dean attempted to comfort Glen who died moments later.
After Glen's death, Madison appeared to be cured. Dean admitted that he felt sorry for Glen who had no more control over himself than Madison did and had no idea of the horrific things he had done. The Winchesters speculated that due to Glen's obvious feelings for Madison, his primal side had turned her in hopes that she would be his mate. However, killing Glen did not cure Madison and at her request, Sam killed Madison to keep her from harming anyone else.