He was portrayed by the late Robin Williams.
Walter Finch is an author of a series of crime novels. After a fan named Kay comes to visit him and they start seeing each other, she laughs at him when Finch is feeling vulnerable. He slaps her to try to get her to stop, but she screams and eventually Finch grows scared and beats her to death. To hide evidence of her murder, he clips her nails, cleans the wounds, then throws her body in a dump.
Detective Will Dormer tracks the killer at a shack in a misty forest, but as Finch tries to escape, Dormer accidentally shoots his partner due to the intense mist. Finch sees this and later phones Dormer at night, who is having serious trouble sleeping. Finch blackmails Dormer into helping him avoid suspicion from the authorities by threatening to reveal that Dormer killed his partner (as Dormer had initially blamed the incident on Finch). However, after another detective discovers the truth about Dormer, he admits what really happened and goes to take out Finch in his shack by a lake. As Finch tries to kill both detectives, Dormer arms himself with a shotgun and sneaks up on Finch during the gunfight. After a struggle, they both end up shooting each other. Dormer is mortally wounded while Finch is killed instantly, and his body falls into the water below and sinks into the darkness.