In God of War Ragnarök, Atreus is revealed to be known as Loki among the giants.
Atreus learns this part of his identity at the end of the 2018 God of War. After Kratos and Atreus spread Faye's ashes in Jötunheim, they discover a mural showing that the giants called Atreus Loki. Ragnarök develops the consequences of that revelation as Atreus searches for the surviving giants and tries to understand his role in prophecy.
The games use the name as part of their own interpretation of Norse mythology. In traditional Norse sources, Loki is a complex figure associated with shapeshifting, trickery, and several major events leading to Ragnarök. The video-game character Atreus is not simply a direct copy of every traditional account of Loki.
The name is also connected to Atreus's mother, Faye, whose giant identity and plans are important to the story. Kratos remains Atreus's father, while Loki is his giant name.