My favorite is Bog king from Strange Magic - Has a song talking about how evil he is. But all he does is prevent the spread of dangerous mind control magic, and quarantine people under the effects of said magic. Yes he greatly annoys people doing so, but honestly? If I get hit by a love potion, please quarantine me.
I know hating on League is in vogue in some corners of the internet, but I really like Veigar. He claims to be the master of evil but hates that nobody takes him seriously because he’s short and he takes umbrage with that. His voice lines are quite fun.