Belasco is one of Earth's most powerful sorcerers with an encyclopedic knowledge of occult spells from a number of books. He has a superhuman demonic form, is immortal, and has superhuman durability. He was a 13th century sorcerer from Florence, Italy who contacted the Elder Gods and made a pact with them. He kidnapped Dante's beloved, took her to Pangea, and raped her to produce a new race of demons. When she died giving birth, an enraged Dante attacked him and during the fighting he ended up being placed in suspended animation.
In the late 20th century, the volcanic mountain became active, releasing Belasco. During his attempt to repeat history with Ka-Zar's wife Shanna, he ended up trapped in Limbo when Ka-Zar hurls the Bloodstone locket into the volcano. Belasco conquered the demonic pocket dimension of Limbo and then kidnaps 7-yr old Illyana Rasputina (Magik), to use her mutant powers to open a gateway to the Elder Gods and make her his apprentice. The X-Men attempted to rescue her but failed and she remained trapped in Limbo, where he turned her into a demon sorceress. She turned on him, drove him from Limbo and became its ruler.
Belasco became the ruler of the Cat People and later regained control of Limbo. He attempted to wipe out mankind, but his pawn was killed by the Punisher. He later had a contest with the fear-demon D'Spayre to see if they could corrupt the mutant Cable but failed. Later with the aid of the N'Garai, Belasco fought the X-Men but they emerged victorious with Magik's assistance. He later returned to Limbo and regained his domain. Belasco is obsessed with Magik, not only because of her powers but because he has also fallen in love with her.