The X-Men's arch-nemesis begins his transition from cardboard cutout villain to tragic figure in this milestone issue. From October 1981, this is "I, Magneto..."
Our comic begins with Magneto, using his advanced technology, sending a threat to world leaders from around the globe. He demands that every nation dismantle its nuclear arsenals in order to protect mutantkind from getting caught in the crossfire of a nuclear war, or face utter destruction. As he explains to the currently retired X-Man Cyclops and his human girlfriend, Lee Forrester (captives on his island for the past several issues following a shipwreck and powerless thanks to an inhibitor thingie), the funds spent on such weapons could now go to more worthwhile causes, such as combating hunger, disease, and poverty, ushering a new golden age - with mutants ruling humans and himself ruling mutants. Cyclops counters that there will be resistance, and a Soviet submarine, the Leningrad, proves him correct when it fires a nuke at Magneto's island - an attack he easily repels. He then uses his powers to sink the sub, killing all aboard.
The haunted, fanatical survivor aspect of his personality has become such an integral part of his personality that it's carried over to alternate continuities (except for the Ultimate universe), various video games, the beloved animated series from the 1990s, and, of course, the live-action movies, in which he was portrayed by both Sir Ian McKellen and Michael Fassbender. The dynamic between Xavier and Magneto also changed over time, a later issue revealing they had been friends when they were younger, but fell out over their drastically different beliefs. Just as the X-Men themselves have been seen as an allegory for the civil rights movement, the Xavier/Magneto feud has often been compared to the rivalry between Dr. Martin Luther King and the more militant Malcolm X.