Menthor

Silver Age Origin
John Janus was a double agent who was really working for S.P.I.D.E.R., but when he was given the Menthor helmet he gets mental powers, but also a side-effect. The helmet makes him good and the effect slowly becomes more permanent the more time he spends wearing the helmet. He is killed inaction in issue 7.

Silver Age Appearances

 * T.H.U.N.D.E.R. Agents #1-7