Isaac Foster, commonly known as Zack, is one of the main characters in the anime and game series Satsuriku no Tenshi (Angels of Death). He is a tall, scythe-wielding man with bandaged features and a violent, unpredictable personality. Despite his initial portrayal as a ruthless killer, Zack forms a complex and unique bond with the protagonist, Rachel Gardner. His role in the series is pivotal, acting as both an antagonist and an unlikely ally as the two seek to escape the mysterious building they are trapped in.