In Gloranthan mythology, the first Man was created by the gods as a servant. All mortal races are descended from the First Man. Kyger Litor stepped forth from Hell, and mated with terrified Grandfather Mortal to found the race of Trolls. Grandfather Mortal was made to mate with rocks (fathering the dwarves), plants (elves), water (mermen), and so on.
When Humakt's Lover presented Humakt with the power of Death, she asked Grandfather Mortal, Humakt's friend, to be there to help them test the strange new power. Thus, Grandfather Mortal was the first being to die, and this is why all mortal beings die. Chaos may have seduced him or raped him in Hell, after he was dead, spawning broos, but this is speculation only. Grandfather Mortal is represented in some shamanic Ancestor Worship cults as Daka Fal.