Slade was the main villain in Teen Titans. He is one of the few villains who not only played with the minds of his nemesises, he also tries to get them to work for him as his apprentices. This makes him kind of a stalker sometimes in the series, particularly of Robin, Terra and Raven. He’s a pretty dark, diabolical character because of this.
He’s also pretty powerful. He has enhanced fighting abilities and weapons such as a bo staff as his main weapon of choice. Despite being defeated a couple of times such as being apparently killed by Terra, he keeps coming back for more as definitely one of the most persistent villains ever, who just won’t leave.