At the risk of repeating myself (I do that a lot these days) it seems little doubt to me that the most successful comic book series about a villain was Marvel's Tomb of Dracula which brought Bram Stoker's murderous Count into the modern day. The comic was the precursor to what was a horror boom at both Marvel and elsewhere and generated plenty of spin-offs on its own.
Very quickly there was the black and white magazine Dracula Lives! which was full of yarns of the deadly vampire from across the centuries.
Dracula rated his own Giant-Size series, the debut issue of which was titled Giant-Size Chillers and brought into the Marvel Universe the deadly Lilith.
In the spirit of the classic Universal monster movie rallies Marvel also unleashed a comic book featuring the Frankenstein Monster as well as their own distinctive take on the Wolfman as well as the Creature from the Black Lagoon. These are followed by comics like Ghost Rider and Son of Satan, a regular cavalcade of horror and fright.
But all things come to an end, even the nigh-immortal reign of the Lord of Vampires and The Tomb of Dracula series final ended with its seventieth issue. But it was a series by Marv Wolfman and the great art team of Gene Colan and Tom Palmer which was indeed greater than the sum of its parts. Weirdly it was more mature look at comic book storytelling and as it began the monster wave it was also the last survivor of the classic kind.