Most intersting of Super-Villans not for Marvel but all comic book super villans as he is was not simply just "bad guy wanting to take over world". The basis for all his actions were to protect all mutants or mutant-kind he felt and truly cared about mutants and was sometimes ally to his adversaries, the X-Men, thus he could be described not just as a villan but as an anti-hero. But he took extreme approach to Mutants approach to humans which was complete opposite of Dr. Charles Xavier (Prof X). Thus as an analogy which has been stated before, Magneto was like Malcom-X while Prof X was Martin Luther King.

Always the most devious, and arguably the most powerful of the X-Men villains, but still managed to maintain an aura of mystery and a sort of 'friendship' with Xavier.