Mr. Smith (Sarah Jane Adventures)

Mr. Smith is a supposing character in the Doctor Who spinoff Sarah Jane Adventures, and the main antagonist of the season 1 finale Lost Boy, Mr. Smith was through to be a extraterrestrial super-computer, but was revealed to be a living organism call a Xylok (a crystaline species) that embedded into a computer in Sarah Jane's attic to help her protect the Earth from alien threats.

Personility
Mr. Smith was shown to be helpful, loyal, supposing to assist Sarah Jane Smith by giving her database of alien life-forces and new reports of disturbed events, always follow her orders without hesitation, showing to be benevolent entity who seek to protect humanity. However, Mr. Smith's true nature was revealed to be a sinister, manipulate, murderous, arrogant, evil, insane, malevolent entity who wants nothing more, but the survivor of his own race by crashing the moon into Earth which crack the planet like a egg and released other Xylok that been trapped in the Earth's core for 60 million years. Mr. Smith have no regard of killing billiion of people just to save the Xylok suggesting that his species are better and will do so mush more than a human.