The fourth planet from the sun.
In January-February 1950, Superman journeys to Mars to help actor-director Orson Welles smash a plot by the Martian dictator Martler to "blitzkrieg the solar system" and conquer the Earth (S No. 62/1: "Black Magic on Mars!").
Mars is not only inhabited by little green men, but also by humans that had fled Earth after learning their continent was doomed. This civilization is ages ahead of Earth and have mastered things like: attracting and harnessing comets for heat and power, and predicting weather with their 'XN theory of weathercasting'. They also have Marsboy to protect them, a super-hero parallel to Superboy (SB No. 16/3, "Superboy on Mars").
In April 1956 Superman journeys through the time barrier to the thirtieth century A.D., where he attempts to apprehend a gang of "mystery-thieves" responsible for a rash of spectacular "scientific thefts." At one point, after Superman has intervened in an attempt to prevent the criminals from stealing some "giant robots" from the planet Mars, the villains callously smash the gates on the Martian canals, thereby threatening the immediate depletion of the Martians' entire supply of "precious water" and forcing the Man of Steel to abandon the hunt for the criminals long enough to repair the damage (Act No. 215: "The Superman of Tomorrow"). (See Superman of 2956; Vinson Vail)
In July 1958 Superman journeys to Mars to obtain an ancient statue from the ruins of the planet's extinct civilization. The statue is one of a series of so-called "space trophies" which the Man of Steel gathers for inclusion in a time capsule which the Metropolis Museum plans to bury in the ground as a gift for the people of the fiftieth century A.D. (S No. 122/1: "The Secret of the Space Souvenirs").
In a Decenber 1958 chronicle, Superboy is shown being exposed to Red Kryptonite for the first time by a green-skinned alien named Kozz who claims to be a native of the planet Mars (Adv No. 255, Dec 1958: â€œThe Splitting of Superboyâ€).
In March 1986, in an imaginary sequence of events, the infant Kal-El's rocket lands on Mars instead of Earth. There, the super-powered baby is discovered by a group of Martian warriors and named "Skagerrak." After growing to an adult "warrior" himself, he then becomes the leader of the Martian civilization and eventually leads an assault fleet of "ships, saucers, ... and personnel carriers" to Earth. Once among human-kind, however, he comes to learn the nature of humanity and switches sides to become Superman and to help Earth repel the Martian invaders (S No. 417: "Warrior of Mars").