In the Poetic Edda poem Grimnismál, Odin speaks while disguised as Grimnir.
Grimnismál, whose title means “The Lay of Grimnir,” presents Odin in disguise as a wandering figure. King Geirröth captures and tortures him, believing him to be an enemy or mysterious stranger. Odin refuses to identify himself at first, and the king has him held between two fires.
During the ordeal, Odin recites a long speech describing the structure of the mythological world. He names divine dwellings, explains aspects of Yggdrasil, lists sacred rivers, and gives several poetic names for gods and beings. The poem’s catalogue of names and places makes it an important source for reconstructing Norse cosmology.
The disguise ends when Odin reveals his identity, and the poem’s narrative closes with Geirröth’s death. Grimnir is therefore not a separate god or a permanent alternate identity: it is the name Odin uses while concealed. The poem survives in the Codex Regius, the principal manuscript of the Poetic Edda.