Isaac (Zack) Foster (アイザック・フォスター Isaac Foster) is the deuteragonist of the game, manga, and anime, Angels of Death. He is a tall, 20-year-old serial killer on the run who encounters Rachel Gardner as they collaborate to escape a building.

Zack is impulsive and prone to violence. He is chaotic, quick to anger, and doesn't hesitate to use foul language in any situation. When he feels the urge to kill, he becomes giddy and uncontrollably violent. He struggles to control his murderous impulses. Zack has come to terms with being seen as a monster due to his appearance and violent tendencies. While he has no qualms about murder and destruction, he considers dishonesty immoral, often expressing his disdain for liars.