The X-Men (1963)

[Perpetual Man]

Hmmm, Magneto has always worn the same kind of helmet but there is no mention of it being a defense against telepathy until a lot later on. I'm not certain exactly when, but I'm pretty certain it becomes one of those retroactive plot points, fixed by - as you say - because he knows Professor X.

Just like Juggernaut when I think about it...

 

[Perpetual Man]

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