When the blinding rays of an asteroid reach Mars, the "supra-universal" rays give super-powers to a boy named Sutri. He decides to "use his powers for the good of his people" as the costumed adventurer known as Marsboy.
Martian scientists tell Marsboy that they have discovered that their people originally resided in the lost continent of Mu (which is later identified as Atlantis) on the planet Earth and had fled to Mars after learning it was doomed. Also, they needed a formula for making water that resided in the Sphinx on Earth, so they could save Mars from doom. After battling with Superboy to get it, Superboy tells Marsboy the contents of the secret document hidden inside a copper container that Marsboy's x-ray vision can not penetrate.
Marsboy's secret identity is Sutri, but he uses the alias "Joe Mars" while on Earth (SB No. 13/1, May 1950: "The Boy From Mars").
When Superboy takes a vacation, Marsboy challenges him to exchange places to prove that living on Earth is easier because it has a simpler civilization. After having lots of problems and almost exposing their secret identities, they change back (SB No. 16/3, Sep/Oct 1951: "Superboy on Mars").
Marsboy is almost identical to Superboy except for the following things: