An iconic part of the Master of Magnetism's appearance, Magneto is rarely seen without his ornate red and purple helmet. Technology wired into the inside of the helmet blocks out all but the strongest telepathic attacks.
In Other Media
Magneto (played by Ian McKellen) uses his iconic helmet in X-Men, X2: X-Men United, and X-Men: The Last Stand. As in the comics, the helmet is shown capable of blocking out telepathic intrusion, namely from Professor X and Jason Stryker.
X-Men: First Class
The origins of the helmet (or at least the original one) are revealed in X-Men: First Class, where it is shown that the helmet was initially given to Sebastian Shaw by the Russian military as a gift to celebrate their collaboration. At the close of the film, a young Magneto kills Shaw and claims the helmet for himself, which he later paints red. It is unknown if this is the same helmet worn by the older Magneto in the original trilogy, as it differs drastically. in shape and color.
X-Men: Days of Future Past
The helmet reappears in the sequel, X-Men: Days of Future Past, where it is shown as part of a collection in the Pentagon. The helmet was taken from Magneto after he was arrested and imprisoned by the U.S. government, but he reclaims it. The helmet's color scheme and ornamentation is once again shown to have changed.