Gallaxhar

Gallaxhar was an evil overlord originating from an unspecified species from an planet which he failed to mention the name of to anybody in Earth's general vicinity. He claimed to have suffered several traumatic experiences during his youth, which is the cause of him being driven to destroy his own civilization and proceed to rebuild it on another planet in his own image. Upon discovering Earth, he chosed it as a suitable home. He was capable of breathing a nitrogen-oxygen atmosphere of the exact composition of Earth, indicating that he would not likely need to "terraform" the planet to overtake it.

He was obsessed with a mineral or element known as Quantonium, which he used to power his immense cloning facility. These clones as well as immense robot probe-transports are his main lines off offense, although his starship is also capable of a very powerful homing attack, and also utilizes a tractor beam technology, as is commonly seen in starships. Gallaxharian clones are apparently quite unobservant, as they do not notice monsters dressed up in their clothing minus one, whom they believe is simply a defective clone which they order to be incinerated and thereby disposed of.

He and all known copies of himself were destroyed when his starship self-destructed, thanks to several of Earth's residential monsters hot-wiring the ship's power core. Because of this, his entire species is now presumably extinct.

Trivia

 * While his homeplanet is (presumably) shown at the beginning of the movie, it is not given an official name. He does mention the "High Senate of Maxilon" in a novelisation of the film, however.
 * Not all of Gallaxhar's species are evil. He states in the movie that there were many innocents on his planet before it was destroyed, and in the novelisation goes on to reveal that he was considered a lunatic and psychopath by his people, and may have been found guilty of high treason.