M. Bison – Street Fighter series
The leader of the mysterious Shadloo organisation, M. Bison (known as Vega in Japan) has been a staple ingredient of the Street Fighter series since Street Fighter 2. For proof of the evil dictator's insanity, all you have to do is win a few rounds with him. "Your despair feeds my power!" he sometimes shouts; other times he taunts his defeated foe with the immortal line: "That was delicious!" Even his special moves are based around his mentally unstable tendencies; the powerful Psycho Crusher being one of his signature moves. Bison may be a psycho, but he's a composed and calculated psycho – the worst kind to be up against in a fight.
Psycho Mantis – Metal Gear Solid
"So...you like Castlevania, do you?" Psycho Mantis taunts in one of the most memorable boss battles of all time. How the hell does he know that!? This gasmask wearing loon can't actually read my mind can he!? Well, not quite, but FOXHOUND renegade Psycho Mantis can certainly read something: your memory card, and if there are any Konami save games on there, he'll know. It wasn't just this that gave Mantis an unnerving edge, however; after delving too far into the mind of a serial killer in an interrogation, Mantis adopted his appetite for killing, and became psychotic himself as a result. The gas mask that hides his disfigured face only adds to Mantis' deranged persona.