1. Red Skull
An evil straight out of nazi Germany. This villain is pure evil. He named his own daughter Sin what does that say of him?
I would recommend the avengers: red menace, red skull evil incarnate and the brubaker run of captain America (the beginning of his run).
The Joker is one insane individual. He's obsessed with the Batman and consider him as his playbuddy. He killed, terrorized and dissabled (Barbara) the citizen of Gotham City.
3. Black Hand
William Hand was even as a kid obsessed with death, he killed animals of the neighbourhood and stuffed them as an adult his obsession became even worse.. As an adult he visits his family home kills his entire family and commits suicide. He's then chosen as the first black lantern and almost destroyed the entire DC universe in the blackest night.
Cletus was allready a serial killer before the symbiote bonded with him. With the ultimate weapon sticking to his skin, he slaughters and kills everyone standing in his way.
The assassin who made it his personal mission to destroy Daredevils life. He killed his girlfriend TWICE! and kills radomly whitout any second thoughts.
6. Mr. Zsasz
What's going on in Victor Zsasz is a mystery for everyone. He kills his victims (in his thoughts releasing them from life) and marks his skin for every dead individual. Zsasz is keeping a special place for his friend Batman.
7. Norman Osborn
Norman Osborn is the archenemy of Peter Parker. He throwed Gwen of a bridge and scarred Peter for life. He's insane and suffers from severe Schizophrenia.
8. Mad Hatter
This villain kidnaps women and girls who looks like Alice from Wonderland. Jervis thinks he's the reincarnation of the original hatter and he has to find his Alice when he discovers that the woman is not the real Alice he kills her. This villain is really as mad as a hatter.
A nightmare to Wolverine also a brutal killer. He killed Wolverine's girlfriend and raped her. Crazy dude.
10. Mr. Sinister
A crazy scientist, he uses mutants for his crazy experiments and tormented the Summers family for ages.