Oh dear L. Ron burning in Hell, I've just found something even dumber than the Xenu story I've known and loved for ten years. Here's the summary I just added to the Wikipedia article:
A Marvel Comics villain called Xemnu the Titan featured in Journey into Mystery #62 and #66 (November 1960 & March 1961), as a prototype of The Hulk; Marvel widely reprinted these stories in early 1967  . The Xemnu tale features similar themes to Hubbard's Xenu story: an alien warlord, escape from prison, mass death, telepathy and mental possession of other bodies  . A different Marvel villain called Zemu or Xemu appeared in Strange Tales #103 (December 1962) and Fantastic Four #158 .
I particularly recommend the Operation Clambake Message Board link where someone discovered this and others tracked down every similarity. Oh God. It's even dumber than it looks. Oh God.
(Please do link this post anywhere you may consider suitable.)