Fistandantilus was a powerful dark mage living before the cataclysm. As Raistlin was passing the Test at the High Tower of Sorcery of Wayreth, Fistandantilus made him pass trough the Test, but took some of his life in exchange. Raistlin was left even weaker than before, golden skinned and with eyes as hour-glasses.
Fistandantilus wanted to become a god, so he cast a portal trough the Abyss, but as he was casting the spell, an insignificant halfing used a powerful artefact nearby. This caused a gigantic explosion, in which Fistandantilus's body was destroyed. Unfortunately, his soul did not die, and it is still here as I talk to you, searching for a new victim.
Raistlin, becoming a powerful mage, travelled back in time until pre-cataclysm, where he defeated Fistandantilus once and for all, taking his essence to even grow his powers. This was the end of Fistandantilus.