Some people say they can discern elements of this in the Lee material: my colleagues at Children of the Atom say that Magneto and Xavier's telepathic battle in #4 is hinting at it. I can't agree, as Lee's run was simply not that subtle, and it wasn't shy of giving backstories when it wanted to: see the Juggernaut, Lucifer, and so on. But I will agree that Lee/Kirby's depiction of Magneto was certainly conducive to what Claremont later did. It worked out fabulously.
Let's see what we've had over the years.
|X-Men #4||Magneto rescued Quicksilver and Scarlet Witch from a mob in central Europe.|
|X-Men #125||Magneto had a wife called Magda, whereabouts unknown. No mention of children.|
|Avengers #186||A woman named Magda fled to Wundagore after her husband manifested powers and proclaimed his superiority to normal humans, where she gave birth to Quicksilver and Scarlet Witch.|
|Uncanny X-Men #150||When Magneto manifested, he was avenging his and Magda's murdered daughter, Anya. |
He had been an inmate at Auschwitz.
|Uncanny X-Men #199||Magneto saved lives during the Holocaust.|
|New Mutants #49||Magneto survived a firing squad that killed his parents, (by use of his magnetic powers?)|
This is all skillfully woven together in this in Classic X-Men #12. The framing story is set just after the events of X-Men #104, in which Magneto is not so much defeated by the X-Men as abandoned by them. Magneto recuperates in a hotel room, and remembers his life with Magda. They had escaped from Auschwitz soon before the war ended (dovetailing with the end of Magneto Testament), survived, and when the war was ended moved to Ukraine, with the idea that Magneto might go to university. Unfortunately, unscrupulous gangmasters kept taking commission and Magneto got angry. Crowbars were flung. Magnetokinetically. Oops. He then went back home, noticed his house was burning down, and is arrested while he would quite like to save his Anya, please. He lashed out, burning everyone, much to Magda's horror. She ran off, while he went on to become a mutant terrorist.
Except: in the present day, he's watching a house burning down with a mother and daughter inside.... He saves them. Not all evil then.
There's not much here we didn't already know, but it's still nice to actually see it happen, and the framing story sets up his later reformation. Yet, he's still going to act like a Silver Age villain for a few more encounters with the X-Men (in the reprints: he's already well on the wagon in the 1987-current comics). He needs time to work things out.