Spawn is one of the most successful independent comic book characters, and a huge reason behind the initial success of Image Comics. Born from the mind of artist Todd McFarlane, the character and his horrific mythology combine Eldritch horror, slasher movies and the faint smell of superhero comics. For as powerful as Spawn is, it's only fitting that he has equally as deadly enemies.
The most well-known of these is the Clown, a corpulent and vulgar jester who's actually the unholy demon known as the Violator. Despite how popular that character is, he isn't Spawn's true arch-nemesis. Forcing Al Simmons into a Faustian deal and threatening him every step of his undead life, the devilish Malebolgia is the true face of evil behind the story of Spawn.
The Devil You Know
Like the title hero himself, Malebolgia first appeared in Spawn #1. Revealed by laughing at Spawn's confusion in the first issue's ending, his name is derived from Malebolge, the ditches in the eighth level of hell in Dante's Inferno. Fittingly, he's the demonic overlord that Al Simmons made a deal with in order to come back to life and see his wife Wanda again. Malebolgia isn't the only ruler of Hell, or the true devil, but he's incredibly powerful and has waged war with the forces of Heaven for over 70,000 years.
Malebolgia was created from necroplasm, which is also the finite energy source of Spawn's own power. Malebolgia never lets Spawn forget this, constantly reminding him that when his power runs out, he'll be a servant of Hell forever. To play with his slave, he purposefully clouds Spawn's memories, hoping to further corrupt him into the ultimate killing machine. Thus, not only is he the reason for the meandering mystery of the first few years of the Spawn comic book, but he literally caused Al Simmons to be Spawn in the first place. This central role in the mythology saw him appear in the live-action movie, where he was voiced by none other than Frank Welker, who also famously voiced various characters from Scooby-Doo and Transformers.
Hell Hath No Fury
This relationship makes Malebolgia Spawn's arch-rival much more than Violator. For one, Violator, while slightly more iconic, is only Malebolgia's minion. His ridiculous and petty antics are many times brought to heel by Malebolgia, who chides him for his foolishness. Likewise, for as powerful and resourceful as the Violator can be, his power is only a fraction of Malebolgia's.
As mentioned, Malebolgia is the very reason for the franchise even existing. If not for him, Al Simmons would have never been tempted to inadvertently be reborn as a Hellspawn. In fact, Malebolgia had been shaping events in Simmons' life to make him into a better, more merciless soldier. This shows how the downfall of Simmons' tragic life was essentially at the hands of Malebolgia, with Clown/Violator really having nothing to do with this ambition.
Finally, the first 100 issues of the book all built up to Spawn eventually facing Malebolgia once and for all. Clown may have once been a formidable opponent, but once Simmons found his bearings as Spawn, he was more of a nuisance than anything. The final showdown with Malebolgia involved Spawn gaining more power than ever to face his enemy, and he only gained more power after doing so. Malebolgia would later return in the form of the Freak. This speaks to the volume of Malebolgia's terror and how much more fear-inspiring he is, as well as how much of a joke Violator had become by that point. Though he's yet to show up in the book's current events, the ruler of the 8th level of Hell will always be the one villain to define Spawn more than anyone else.