Belasco was a sorcerer in 13th Century Italy who used his knowledge of alchemy and the black arts to contact the "Elder Gods" (actually extradimensional demonic entities known as the Mabdhara, masters of the N'Garai). He forged a pact with them enabling them to cross the barrier to our dimension using a pentagonal arrangement of five Bloodstones. In return, Belasco was granted immortality and immense mystical power. He was also given a demonic appearance, as he was intended to form a new race of Earth-dwelling demons.
As part of the Sorcerers Guild he opposed Ebrok's creation of the Cat People. The group banished the Cat People to the other dimensional netherworld of the Land Within.
Belasco's early history was told by the poet Dante, though there was some dispute as to the veracity of these accounts. To this end, he kidnapped Bice "Beatrice" dei Portinari, beloved of Dante, to give birth to the first of this new race. He fled with her to the Atlantean outpost of Pangea, where the Elder Gods directed him to Mt. Flavius, where their summoning ritual could take place. While en route, Belasco raped Beatrice, and she was nine months pregnant by the time they arrived. He embarked onto the island, closely pursued by Dante, and took Beatrice into a network of underground passages designed to resemble Hell. Dante found them just in time to witness Beatrice dying in childbirth and, enraged, he attacked Belasco. During the battle, a pipe was accidentally struck, releasing an unknown liquid that placed Belasco in suspended animation. At some point on the island, Belasco also lost the locket containing the Bloodstones.
In recent years, the volcano mountain became active again, releasing Belasco. He quickly located the locket and found a new sacrifice, Shanna O'Hara. He placed her under his mental control and began the spell. However, just as he was almost finished, Shanna's mate Ka-Zar appeared and hurled the locket into the volcano, sealing away the Elder Gods and apparently destroying Belasco.
However, he instead was trapped in Limbo, where he spent his years conquering it. Once complete, he drew the X-Men to him with the intent to use Kitty & Illyana as means for his freedom of limbo and his Elder Gods' access to Earth. They all managed to escape save the seven-year-old Illyana Rasputin, whom he made his apprentice. He shaped part of her soul into a Bloodstone, giving her great potential for power and allowing him to control her. However, upon reaching the age of fourteen, she rebelled against him, driving him from Limbo. Now its new master, she returned to her own world only seconds after the X-Men had returned, and shortly after joined the New Mutants as Magik. Magik was later deposed as the ruler of Limbo by the demons S'ym and N'astirh, the latter of whom was destroyed, and also restored Illyana's lost childhood.
Belasco eventually took control of Limbo once more. The cultist Sammy Smith, alias "the Rev" (a Jim Jones analogue) worshiped Belasco as Lucifer. The Rev fought the Punisher twice, the second time alongside the Punisher's longtime foe Jigsaw. When the Punisher killed Jigsaw, the Rev used his Belasco-granted powers to resurrect the thug, although both were defeated despite Smith's gift of demonic magic.
Belasco also turned Alpha Flight ally Witchfire against her team by influencing her demonic side. She finally was restored to normal and returned to Beta Flight, Alpha Flight's support group.
It was strongly suggested that Belasco is Witchfire's father or at least that Witchfire believes so.
Later, Belasco and the fear demon D'Spayre contested to corrupt Cable, the son of Madelyne Pryor, who had been the ally of S'ym and N'Astirh. Belasco banished D'Spayre and summoned himself, Cable, and Cable's ally Lee Forrester to Limbo, where S'ym threw Belasco out of his way and fought with Cable. Cable won, and he and Lee returned to Earth.
It was eventually revealed that Illyana's best friend Kitty Pryde had received Illyana's Soulsword after Illyana had died; in dying, she had bonded the Soulsword to Kitty's own essence. After Kitty's team Excalibur fought off several claimants to the sword, Nightcrawler's girlfriend Amanda Sefton was given the sword. She then gave the sword to her mother, Margali Szardos, who was in turn kidnapped by Belasco and brought to Limbo. Nightcrawler and Sefton freed her, and Sefton secretly took the sword and adopted the code-name Magik for herself. Belasco and his allies, the N'Garai demons, fought the X-Men again soon after, but were defeated by the X-Men with the assistance of the new Magik, who revealed herself to be Amanda Sefton.
Belasco had been cast into an even lower level of hell by his disappointed gods, but was eventually able to ritually sacrifice a low level demon to regain access to the Limbo dimension after looking in on Earth and seeing a version of Magik alive there. Belasco fought and defeated everything that the new Magik, Amanda Sefton, threw at him and cast her out of Limbo. Belasco was unable to find Magik alive again on Earth but sensed her presence on the New X-Men (who were unaware they had encountered her when the Scarlet Witch altered the world).
Belasco questioned and tortured them, during which it was revealed that Belasco was also seemingly in love with Magik as well as desiring her powers. Belasco was eventually defeated by the partially resurrected Illyana, once again having become Darkchild and lacking a soul, alongside Pixie who stabbed him with her Souldagger.
Satana visited the Apache Diamond Casino and took part in a high stakes poker game with what she thought were collegiate nerds. But it was revealed that they were Belasco, Mephisto, Asmodeus, Dormammu, and Lucifer in disguise. She lost her soul during the game so enlisted Deadpool to help get it back. He attacked the gamblers cutting them to pieces and revealing their true natures. Satana found a loophole and married Deadpool to break the deal, they tried to kill Deadpool but due to his healing factor they couldn't break the "Till death do us part" clause.
When the Chaos King confronted Marduk Kurios to steal his power, Belasco joined the Hell Lords and many other Demons, but they were defeated. He returned to his throne when Hercules defeated the Chaos King.
