Martians (War of the Worlds)

The Martians are the chief antagonists of the War Of The Worlds book and the varied books, musicals and other works based on it - originally an unstoppable force that almost succeeded in wiping out humanity they are famous for being defeated by the common cold, a virus that while relatively harmless to humans seems to be fatal to the Martians.

Origins
The Martians originate from the planet Mars, a planet long rumored to host life but dismissed by scientists - as they said "the chances of anything coming from Mars are a million to one", however the scientists were wrong and Mars was indeed populated - by alien beings that looked upon their closest neighbor (Earth) with envy and began to plot against the creatures that inhabited it.

Reason For The Invasion
Although it is never specifically stated why the Martians attacked Earth in the story it is suggested that they were envious of humanity and the Earth itself, which was full of life - in stark contrast to the barren wasteland that is Mars. Also due to their highly-advanced intelligence and warlike nature it is possible the Martians deemed humanity unworthy of the planet and decided to take it over for themselves.

Another reason for the invasion, which is explored more in the book than the original film, is that the Martians were also vampiric in nature and were harvesting humans for their blood (this theme was somewhat explored in the most recent version of the movie).

Personality
Ruthless and beyond reason, the Martians were depicted as much a force of nature as alien invaders and had obviously been preparing their assault for years as they easily decimated the nations of the world and were virtually unstoppable until they became ill - the Martians hid most of the time inside their fearsome war-machines and didn't communicate with humanity outside of merciless killing and thus they were probably xenophobic or simply so advanced they viewed humans as unworthy of communicating with.

They were however extremely intelligent and masters of war and seemed to have a masterplan on a greater-scale than they ultimately achieved - it is possible that had they not caught the common cold they could of wiped humanity out and begun a search for other worlds to take over.

Impact On Other Works
The War Of The Worlds is considered a classic of science-fiction and the Martians remain one of the most popular alien invaders in fiction - although the popularity of Martians has begun to decline somewhat since the craze of X-Files style Grey aliens took over, however the Martians still enjoy considerable popularity - especially in Japan.

The story of War Of The Worlds and the Martians in general are also inspirations for innumerable stories and cartoons as well as parodies - some famous examples being the series Tripods and the Looney Tune villain Marvin The Martian.