History
As a child Magneto was saved from a concentration camp by Captain America, this led him down a different path and seemingly founded a school to help Mutants.[1]
Magneto was the only survivor when the X-Men were massacred at Magnus' Academy for Gifted Youngsters by S.H.I.E.L.D.. When the Avengers came to the Academy, Magneto attacked them and then left vowing vengeance against humans.[2]