Upon debuting, The Space Phantom claimed he was a member of an unknown alien race, coming to Earth to defeat the Avengers as a means of testing if the planet could be invaded by his people. Taking the shape of several Avengers, he tried to sow dissent amongst their ranks. He was defeated when his power backfired, trying to duplicate Thor, sending him to Limbo.
From: The Avengers #2 (1963)
Through subsequent appearances, this classic “extraterrestrial invader” origin has proven something of a falsehood. At one time, The Space Phantom claimed to be a citizen of the planet Phantus as an elaborate hoax when truly he is a denizen of Limbo. In fact, the identity of “Space Phantom” isn’t that of an individual being but more of a generic term given to the trans-formative state wherein anyone lost for duration in that timeless nonplace can physically and mentally become one.