Sinmara was once the most credible of the few threats to Surtr's position as warlord of Múspellsheimr only for word to reach the other Nine Realms that Sinmara's coup had been aborted to accommodate her wedding to Surtr instead. With the marriage she became step-mother to Glöð and Eysa, both of whom she regarded with thinly veiled contempt.
Sinmara is usually considered a consort to the fire jötunn Surtr, though she is actually the wife of Mímir. She is attested solely in the poem Fjölsvinnsmál, the second half of the two-part compilation titled Svipdagsmál, where she is mentioned alongside Surtr and named as keeper of the legendary weapon Lævateinn.
- Assassin's Creed: Valhalla – Dawn of Ragnarök (first appearance)
- Assassin's Creed: Valhalla – Forgotten Myths (mentioned only)