Nearly everything in the Magneto bio is from the comics. Some things are additional details derived from historical or scientific facts. For example, Magnus served in the Auschwitz Sonderkommando, as was shown in UNCANNY X-MEN #274, and stated in the 2004 EXCALIBUR; knowing Auschwitz history and the history of the SK, one can describe a lot more of what young Magnus was forced to do for the Nazis than is explicitly stated in the comics. As it is, Magneto himself has described what he did, basically, in UNCANNY #274, but that is an example. Likewise, dealing with Magda and Magnus' escape from Auschwitz as shown in the back-up story "A Fire in the Night" from CLASSIC X-MEN #12; the events depicted happned on a particular day in history, under certain circumstances. John Bolton's art and Chris Claremont's story don't have to show ALL these circumstances and details for us to know they happened ... had to have happened. In any case, I tried to keep the details of the BIO to those that appear in the comic.
In the 2004 EXCALIBUR, Claremont retold the story of Magda and Magnus' escape and early life, and he left out the part about the Carpathian Mountain village. This is clearly shown in "A Fire in the Night" and since it is canon, Claremont's 2004 omission doesn't really contradict it. Claremont's EXCALIBUR reference jumped from the escape, to life in Vinnitsa. His earlier story described (logically, since they were on foot in the dead of the winter of 1944-1945) how they found shelter and safety in this obscure village BEFORE they moved to Vinnitsa.
As to Sabra, and her motivations, see X-MEN #73.
Another thing editors and fans seem to continually get mixed up is that Magneto did NOT reverse the poles in Magneto War -- he built this machine to channel his powers in order to disrupt and destroy the magnetosphere of earth. It was a crazy threat -- a blackmail attempt -- that went wrong, when he lost control of the situation after the X-Men attacked him.
Magneto is Jewish, there is no doubt about it. It was even stated in X-MEN #112, and EinC Quesada has backed this up. See X-MEN #72 for Magneto's confrontation with the forger Georg Odekirk. Go here for references, that include scans (fair use, fair use) from the comics to illustrate the references.
Another point that needs clarifying -- in the excellent Magneto bio that appeared in the most recent HANDBOOK OF THE MARVEL UNIVERSE 2005 -- written by Eric Moreels -- there was only one mistake. And I've addressed that in this BIO. That being, Moira MacTaggart did NOT genetically "make Magneto good." That's simply not what happened, as stated in X-MEN vol.2 #2. And it's not a good position for Marvel to take -- that people are genetically "good" or "evil". Marvel has always been about character complexity; heroes have flaws, villains aren't all bad. Magneto's flaws are many, but he was basically a good man who went bad -- or continually makes the wrong choices, and is constantly goaded by his traumatic and painful past. Moira did NOT make Magnus good; she states exactly what she tried to do. She says that Magneto had an instability in his physiology that meant his human body couldn't handle the immense power he tried to channel through it. His mind, his psyche, were affected. We've seen in the comics (UNLIMITED #2, one of the parts that was actually accurate) how Magneto has an extra tract (or bundle of neurons) between his midbrain and brain stem. Moira tried to genetically strengthen his central nervous system, his body -- tried to "correct the anomaly" is her exact wording. The anomaly being, here is this uber-powerful mutant with a body that can't handle all that energy and power.
In any case, Magneto "made the choices he would have many anyway" as Moira told him. He, Magneto, was the one who accused Moira of "brainwashing" -- and he wouldn't let her protest or explain.
Astra did not "clone" Magneto. I know it's a fine distinction. But she made a bioengineered copy; Magneto was scanned and Astra copied him down to the last cell part, and reproduced him in a younger, more pliable version.
Magneto was advised by Storm to join the Hellfire Club. He was unsure of what to do, when he got the invitation. She said she'd join with him, as co-White King. (Yeah, "king" -- which is very intersting.) But then she and the X-Men appeared to die in Fall of the Mutants, and Magneto got sucked into the Club by Emma Frost's machinations.
Magneto has stated that when he was reaged by Davan Shakari, he was returned to his "prime." And in several stories commented on how young and healthy he was. We see he was sucked almost dry and was weak and aging in Neal Adams' UNCANNY #63, where he's the "Creator" in the Savage Land. And, in AVENGERS #110 and #111, he has to use a trick uniform that he gave to young Warren Worthington that transfers the youthful energy from Angel to him. He can harldy even move, let alone use his powers. It was a recurring theme -- he was destroying himself with his powers, and had to repeatedly "recharge." ALso, there are repeated references in these old stories to Magneto's insanity. Jack Kirby drew those eyes differently than he did the faces of other villains -- Magneto's eyes were crazy and wide and staring, circled by dark lines. Magneto was described as having "insane laughter" or was simply described as being "insane." Not all Marvel villains back then were so described. Certainly not Dr. Doom, for example.
I go into this kind of detail to point out, that after he was babyized by Mutant Alpha, who did this specifically to give him a second chance, knowing he was basically a good man who might be able to change, he was supposed to grow up naturally, his body healed. When he was rapidly reaged -- passing through all the growth stages in minutes as is shown in the comics (UNCANNY X-MEN #104) -- to end up a man in his early 30s, his body regenerated itself at an incredible rate, and he healed all the damage of his body in those parts of his body that can regenerate cells and be repaired! This is scientific fact. It is also a handy explanation as to why Magneto continued to act psychotic for a little while AFTER he was reaged.
Neurons don't regenerate. When damaged, they are lost forever. That's why brain damage is so devastating. The brain DOES however, "rewire" itself -- reestablish new connections. People who are brain-damaged can relearn, they get their memories and skills back with effort. This being a science-fiction comic book story, we can see IN THE COMICS that Magneto was reduced to the level of a six-month-old baby and he retained much of his adult consciousness. (UNCANNY X-MEN #112, CLASSIC X-MEN #19). And indeed, the baby's brain is almost 50% of it's adult size already. When Magneto was reaged so quickly by Shakari, he gained the full mass of his brain back, through natural growth and devleopment. But he still used those damaged, even infantile parts of his brain for a little while, while his brain rewired itself, and the adult parts of his cerebral cortex were integrated. Or, you could say, he retained from babyhood the more primitive dependence on the hind-brain (limbic system) that made him act insanely for a little while, and like all of us, as he aged his forebrain or cerebral cortex added most of the new growth. Only he aged in a few minutes.
I have reread the comic book Classic X-Men #19, and I found it very interesting. My contributions to other biographies of Magneto seemed fuzzy on this topic, so I wanted to clarify Magneto's activities at this time.
What I found is that the story, "I, Magneto," written by Claremont with art by Bolton did not actually mention WHICH intelligence agency Magneto was working for. The only fact we know is that Magneto was working for the Israeli government, and this is almost certainly as an agent of Mossad.
Magneto names the person he phones from Nazi Hans Richter's demolished fortress, "control." The man who murders Isabelle is identified only as "control" and Magneto's "case manager." The only agency we can really identify as being involved is Mossad, because Magneto makes the clear statement that he is turning his captured Nazis over to Israel for trial, and Mossad was/is the agency that was responsible for making contacts with agents and retrieving Nazi war criminals. (Their most notable case being that of Adolf Eichmann.) So, ironically, after all these years of thinking the CIA was definitely involved in this story, it's actually only confirmed that Mossad is involved! Thus, we are left to conjecture as to who Magneto's control was or controls were.
Another interesting thing is the way Magneto's "case manager" or "control" talks after Isabelle is murdered. He seems British. And indeed, if Magneto had been a citizen of Israel for a number of years, he could just as likely have turned to British intelligence -- MI5 which is military intelligence, or the SIS, or MI6 "The Firm" -- to provide him resources to help track escaped Nazi war criminals. In any case, I think Claremont left that deliberately unclear.
Also, Magneto apparently was "hot-dogging" it (Control -- "... but no ... you had to 'hot dog' it ... go haring off on your own") with this Western intelligence agency's full knowledge. Magneto answers, "That never mattered before." So, Magneto was turning Nazis over to Israel, knowing that his Western spy-masters knew about it, presuming that they didn't mind. Did Magneto presume that they were the good guys who wanted to avoid political complications but that they really were on the same page as Magneto, turning a blind eye as he gave his captured Nazis to Israel? If that was Magneto's presumption, he was very wrong, as he finds out
Magneto's control responds to Magneto's comment, "That never mattered before," with, "That was when you were sanctioning their Nazis. The other side's. Richter was one of ours. A very important asset. You made some waves with that caper, Magneto."
Magneto answers: " 'Ours?' 'Theirs!' What the devil are you talking about?! They're Nazis! War criminals!"
So, Magneto clearly was naive about the political realities. He believed that this intelligence agency he worked for was hunting Nazis for the same reasons he was, and was letting him turn these criminals over to Israel. He was very clearly (a) a double-agent for Mossad but this was not a secret to his control, and (b) Magneto knew they knew he was working for Israel, and didn't think they cared.