MONSTERS ON THE PROWL #11
OTHER NOTABLE APPEARANCES:
JOURNEY INTO MYSTERY #66 (reprinted in MONSTERS ON THE PROWL #14)
MARVEL FEATURE #3
DEFENDERS (Vol. 1) #12
INCREDIBLE HULK ANNUAL #5
MARVEL TWO-IN-ONE #78
SENSATIONAL SHE-HULK #6-7, 4-43
Small-town electrician Joe Harper found the unconscious body of a giant creature in the nearby swamp, and using his electrical knowledge, revived it. It revealed that it was called Xemnu, and had escaped a prison planet. It then used its mental powers to take control of humanity (except for Harper) and commanded a giant spaceship be built for him so that he could return to his homeworld, destroying the earth in the process. However, Harper saw it as an opportunity to destroy Xemnu, and rigged the rocket to shock the alien into immobility. He then sent the ship into an orbital pattern towards the sun, and with Xemnu gone, the rest of the world lost all memory of Xemnu.
The Titan managed to break free from his orbit and returned to Earth, where he sought revenge on Harper. He was defeated again by the human when he attempted to use his hypnotic powers to atomize Joe, but Harper used a mirror to reflect Xemnu's powers back on to himself, vaporizing the monster.
Xemnu next attempted to subvert the minds of children everywhere under the guise of a lovable television character. His ploy was found out by the Defenders (Hulk, Dr. Strange and Namor), and he was driven off. (Marvel Feature #3)
Some time after, Xemnu exacted revenge on The Defenders when he placed the town of Plucketville under his mental control and captured three of their members (Doctor Strange, Valkyrie, and The Hulk). However, the bestial Hulk soon broke free of his restraints and combated Xemnu. As The Titan attempted to escape, Hulk lobbed a small bomb at the alien, which exploded on contact. Xemnu was presumed destroyed (Defenders #12)
Determined to destroy The Hulk, whom had twice defeated him, Xemnu constructed replicas of Groot, Goom, Diablo, Taboo, and The Blip. Even with this army, Xemnu once again was defeated. (Hulk Annual #5)
Still intent on taking over the world via television and other media, Xemnu took on the disguise of movie producer Amos Moses, but was exposed and defeated this time by The Thing and Wonder Man (Marvel Two-In-One #78)
Years later, Xemnu reappeared yet again, this time challenging The She-Hulk, Razorback and U.S. Archer. He had revised his plot, this time focusing on mutating unborn children into beings like him. Once again, he was thwarted, and left in the care of an alien named Enilwen. (She-Hulk #6-7)
Xemnu soon after escaped, but his plans of revenge on She-Hulk were quickly foiled by She-Hulk's associate Weez (formerly known as the Blonde Phantom). (She-Hulk #42-43).
NOTE: Xemnu's appearance, without any purpose or design, went back and forth between an all-furry look, and a more cybernetic one. No explanation was ever given as to why the appearance changed so often.
Also, it should be noted that in his first appearances, he was referred to as Xemnu The Living Hulk, but was retroactively called Xemnu The Living Titan to avoid confusion with another character called The Hulk.