Elias Stilinski is the Sheriff Stilinski's father who resides at Goodwater Assisted Living facility due to dementia.
Elias is played by Patrick Gorman who is best known for appearing as Old Steve Rodgers in Avengers Endgame.
Beforehand, he was an army engineer who had a poor relationship with his son. Noah once tried to stop his father from "going after" his mother and Elias pushed him through a glass table. The incident left Noah scarred and pieces of glass still working their way out of his body.
Like his grandson, his nickname was also "Stiles."
In Sundowning, Scott, Lydia, and Malia visit him in order find someone named "Stiles." Elias believes it is 1976, is confused by their intrusion, and later loses his facilities during their visit until Lydia presenting him with math equations to calm him down.
Regaining all of his senses, Elias becomes condescending towards the teens and insults their parents until the sheriff arrives and orders them to leave. The old man insults him and tells him to crawl back to his dead wife and loser son before becoming confused again.