Thanatos is the personification of Death, son of Nyx and the older twin brother of Hypnos. As the embodiment of death, Thanatos has many duties requiring him to venture up into the mortal realm. His most recent such venture took longer than usual - speculated by Hypnos and Zagreus to be related to the ongoing war - but returns some time after the game's opening. He apparently dislikes the mortal realm, in particular how bright it can get.