Martians (the native inhabitants of Mars) are quite varied.
Not much is known about the Martians' history. It seems that the dominat race was the vicious, aggressive Gargs, which had enslaved the extremely friendly, one-eyed Yorps. According to the Keen 1 in-game story, all the Martians were ruled by a despotic King, who was probably a particularly intelligent Garg.
Under the rule of his King, the Martians were able to create a highly advanced culture. They built roads, towns, cities, and shrines. They even invented teleporters for long distance travel. Though the Yorps were probably good servants for some tasks, the Martians built robots for menial work and guard duties. They created the Butler Robots, probably for jobs such as cleaning and cooking. They also built the Guard Robots, to guard and protect the Martian cities and treasures. Martians also seem to have developed rayguns, though it is not clear how they use them, as the guns appear to need a hand to hold them, and Martians do not possess that kind of extremities. They also seem to have technology to send telephathic messages, which can be seen in the messages stored in statues found inside several of the Martian shrines.
At some point in their history, the Martians developed the ability to travel through space. They contacted other sentient races of the Milky Way galaxy, and learnt the Standard Galactic Alphabet. Apparently their King established that alphabet as the only writing system in Mars, as no other kind has been found (it may be possible that the Martians did not have writing previous to this).
The Martians also started visiting Earth, probably at some moment in the Earth's 20th century. For some reason, they started to develop some sort of religion around Earth objects, specially around human toys. They travelled to Earth to steal hula hoops, skateboards, teddy bears and pogo sticks, all of them seen as holy objects. In particular, the pogo stick seems to be the most holy of them all: there is a special shrine, the Pogo Shrine, dedicated to the toy. They also seem to like Earth food: lollipops, soda cans and pizza slices can be found in Martian cities. This is most likely a result of the traditional diet of Martians which, while unknown, is probably rather sparse given the arid nature of Mars.
In recent years, the Martian civilization has fell into turmoil. In July 20, 1976 (Earth time), the Viking 1 lander arrived to Mars. It was a spacecraft sent by Earth humans to explore the Martian surface. Unfortunately, the ship landed on top of the Martian King, killing him instantly. The Gargs got very angry and fell into disarray, and the Yorps were able to free themselves. Since them, it seems that all Martian cities have become independent, and there is no central authority whatsoever. Robots seem to keep doing their chores, Yorps jump around just being happy, and Gargs run amok trying to vent their anger into anyone they can find.
A few years ago, a group of Vorticons arrived to Mars and established an outpost. It is not clear how the Martians reacted to their arrival, but they seem to live in a relative stability. Because so few Vorticons arrived on Mars, their impact on the lives of the Martians was minimal. In fact, with the exception of the Vorticon Commander's fortress, the Vorticons did not establish any new bases, but rather moved into local cities. Following the destruction of the Vorticon mothership, the outpost on Mars was abandoned. No attempts have yet been made by the current Vorticon leadership to reestablish a presence on Mars, so the limited signs of Vorticon settlement will probably be left to slow decay, or possibly be inhabited by Martians.