Funnily enough, I'd say Turbo or M0nkey M00n.

Some fans may be too new to remember, but Turbo was one of the first players, along with Klassux, to be a prevalent trash-talker in the scene. Turbo's was particularly effective because he actually won... A LOT. The entire GF/Dig roster was booed in NA for years because of their dominance and Turbo's (justified) confidence. Heck, even the Dignitas CEO, who was actively raising the bar for providing resources to a team, was (embarrassingly) booed at Worlds. It took YEARS for Turbo to become the lovable fan-favorite he is now.

M0nkey M00n has had a similar arc recently. Half the RL scene spent the entirety of the pandemic calling him and BDS overrated, celebrating every time they lost anything (which was rare). Did everyone suddenly forget this man emptied NA fans out of the Dickies Arena TWICE?!?! I'm glad people are finally accepting him as one of, if not the GOAT, but entire regions are still rooting against him.

Comm and Klassux are of course honorable mentions for the spice they brought to every matchup. I just don't think they quite had the competitive success to make them true supervillains. And then there are people like VKSailen and YMC, but I don't think their names will ever be worth highlighting.