In God of War Ragnarök, the mysterious artifact sought by Odin is called the Mask.
The Mask is a central plot object in the game. Odin believes that completing it will allow him to look through a rift and gain knowledge of an existence beyond the known realms. He sends Thor and other forces to recover its pieces, drawing Atreus into the conflict.
Atreus becomes involved because he can sense and interact with the Mask in ways other characters cannot. The search takes the characters through multiple realms and becomes closely tied to Odin's attempts to control knowledge and prevent the uncertainty surrounding Ragnarök.
The artifact is generally identified simply as the Mask in the game and reference material. Names such as World Mask or Aesir Mask are descriptive inventions, not its canonical title.