Dennis Stillwell was a Werewolf and former member of the North American Werewolf Pack before deciding with his son to become a mutt in 1982. He was the father of Joey Stillwell and grandfather of Noah Albright. Dennis lived in Alaska with Joey after the leaving Pack until his torture and murder in the novel Frostbitten. He is described as Clay in Savage as being a small man
In the novella Savage he is in attendance at the quarterly Pack meet where Clayton Danvers is introduced to the Pack and becomes an official member. Dennis is described as one of the Pack's peripheral members and greeted Clay with a warm smile. He supported Dominic Sorrentino's decision to allow Clay to join the Pack.
Dennis appears as a Pack member for the last time in the novella Ascension, a sequel to the previous novella. He was one of the participants in a deer hunt and waited 'poised like a setter on point' to feed on the deer. He is not mentioned to have been in attendance at Dominic's last Pack meet but can be assumed to have attended as his son did.
He was present at Dominic's wake and stopped his son from voting for Jeremy Danvers for Alpha, asking for two days to decide. Fearing Malcolm Danvers reaction if they voted for Jeremy, and not believing they'd have much of a place in Jeremy's Pack despite believing him to be the best choice, Dennis and his son left the Pack becoming mutts. Some years later the Pack learned Dennis and son had settled in Alaska and he begun speaking to Jeremy again but never returned to the Pack.