Mars is the home to the Martian race, often depicted differently in various fictional universes. Civilizations on Mars are often depicted as either dead or dying, much like the planet itself.
Mars is one of the solar system's inner planet and is thus comprised primarily of rock. It has an atmosphere, albeit a thin one by Earth standards. It is of similar size to Earth though it is slightly smaller. Consequently it has a weaker gravitational pull; some Earth characters on Mars, such as John Carter, are depicted as being able to leap large distances.
Although generally flat it does have the largest known mountain in the solar system, a volcano named Olympic Mons. There are several famous areas, among them Syrtis Major. The canal like features on the planet's surface have also been the source of numerous works of fiction.
In the DC Comics Universe, Mars was once home to a civilized race that was long ago extinct. It is the home planet of the Martian Manhunter. The Martians themselves referred to the planet as Ma'aleca'andra (the name is a reference to C.S. Lewis's Out of the Silent Planet where Mars is called Malacandra by it's inhabitants.) The Martians are divided into the Green and White Martian races, who are often at odds with each other.
The planet is still an occasional home to the Martian Manhunter, but is otherwise deserted since the near extinction of the Green Martians and banishment of the White Martians.
In the Silver Age, it was depicted as populated up until 1969, when Commander Blanx unleashed the Blue Flame, which drove the remaining Martians to migrate to Mars II.
The Martians in the Marvel Comics Universe were created by the Annunaki, an alien race from a distant star. They were responsible for putting intelligent life on the planet.
The Martians were an advanced civilization that were at war for a long period of time with the inhabitants of Tiamat, Mars' sister planet located between Mars and Jupiter. The war resulted in the complete destruction of Tiamat and Mars becoming a barren wasteland. This made the Annunaki mourn greatly for their loss.
More recently Mars has been turned in to a Garden Planet with it's own ecosystem by Ex Nihilo.
Earth-691 War of the Worlds
In this reality, Martians (similar to the H. G. Wells creation) invade Earth in the 20th century, conquering and killing all of Earth's heroes. After their victory, the Martians return to Mars, only to be stricken with a deadly plague, leaving them virtually extinct. Mars is quarantined for centuries after this event.
Edgar Rice Burrough's novels have been interpreted for comics on a number of occasions, most recently by Dynamite in Warlord of Mars. The planet is called Barsoom by it's inhabitants and it is on the verge of dying. Water is scarce and it's atmosphere is maintained by machines. This was not always the case and the planet still shows signs of it's former glory in it's dry sea beds and abandoned cities. One of the greatest cities was known as Korad. It had been built upon a natural harbor. The saying on Barsoom is "A warrior may change his metal, but not his heart"
There are a number of intelligent races that live on Mars in various levels. Most notably are the "green martians" and "red martians". The two are very different from each other but do carry some similar characteristics.
The depiction of Mars in the John Carter series is generally very inaccurate. Despite the fact of a lower gravity it would not grant John carter the level of the abilities which he experiences.
The Green Martians known as Tharks are a brutal and savage people. They are without pity or compassion, respecting only strength and find humor in the suffering of others. They are much taller than a human, ranging from 12 to 15 feet. They also have four arms and tusks and reproduce by laying eggs which are left away from the city to mature.
They live in tribes and do not form families. Rising up within the tribe's hierarchy is accomplished by killing a Jed, a chieftain. They live in the abandoned cities of Mars and are constantly warring with the Green Martian of other cities as well as the Red Martians. Much of their technology is stolen from the Red Martians as the spoils of war. They use rifles and ride beasts called Thoats in to battle. Green males form the raiding parties while the females maintain their equipment and teach the young males to fight.
Red Martians are very similar to humans in appearance, though they can live to a thousand years old and are, like Green Martians, oviparous. They are advanced technologically, form families, live in city states and they control the canals that cross the planet. They do not wear clothes, only harnesses for equipment and jewelry.
In Alan Moore's Watchmen, Doctor Manhattan teleports to an uninhabited Mars with Silk Spectre. There he visit's Mars's notable features, such as Olympus Mons, and discusses his lack of emotional investment in Earth and helps her realize who her biological father is.
Alan Moore revisits Mars again in The League of Extraordinary Gentlemen, volume 2. This occurs during the events of H.G. Wells's The War of the Worlds and features Martians from that novel as well as the Sorn from C.S. Lewis's Out of the Silent Planet and the Barsoom from Edgar Rice Burroughs's series of John Carter of Mars books. John Carter also features, as he and Lt. Gullivar Jones of Edwin Lester Linden Arnold's Gulliver of Mars also live on Mars. In the book, the humans have formed an alliance with the Sorn and Barsoom to attempt deal with the threat of Wells's Martians who eventually leave for Earth.