Before Professor Charles Francis Xavier and Erik Magnus Lensherr became Professor X and Magneto, the two young mutants worked together to recruit the 1st class of mutants. The Hellfire Club, led by Sebastian Shaw (Kevin Bacon) and Emma Frost (January Jones) plan to start a war, pitting Cuba against the United States (The Cuban Missile Crisis).
The new X-Men were Havok/Alex Summers (Scott Summers' brother), Hank McCoy/Beast, Raven Darkholme/Mystique (later joins Magneto's Brotherhood of Mutants), and Sean Cassidy/Banshee, the Irish mutant with the power of sonic scream/manipulation and flight.
I am planning to see X-Men: First Class, even though the original 5 x-men from the comics are not in it (except for Beast and Prof. X). They put Havok instead of his brother, Cyclops, and there are no Warren Worthington III/Angel and Jean Grey, or Bobby Drake/Iceman.
Azrael, Nightcrawler's father, is in this movie too.