Ras Thavas by J. ALLEN ST. JOHN.
Ras Thavas was born a noble of Toonol, a somewhat self-isolated city-state in the Toonolian marshes (The Master Mind of Mars ). When Vobis Kan, Jeddak of Toonol discovers that his feared enemy the Assassin Gor Hajus has been revived, he assumes Ras Thavas is responsible and drives him from his island.
Ras Thavas then settles in the dead city of Morbus where his experiments in creating life get completely out of his control (Synthetic Men of Mars ). He is rescued from the disastrous fruits of his own genius by John Carter who needs him to treat the badly injured Dejah Thoris. Presumably Ras Thavas continues to practice his art in Helium.
Ras Thavas is probably one of the oldest living Red Men. At the beginning of the series most Red Men (and Green Men) pay at least lip service to the religion of Issus and voluntarily undergo the pilgrimage down the River Iss upon reaching the age of 1000 (presumably Barsoom years, corresponding to about 1881 Earth years). They are still physically more or less in their prime at that age, whereas Ras Thavas is near death from old age at the beginning of Master Mind.
Characterizing him as a villain is not entirely accurate; he is almost entirely disinterested and dispassionate and for the most part he doesn't want to kill other people or rule over them. This same disinterest in their welfare also means that he won't hesitate to perform unethical experiments on them (including some that might be harmful or fatal) if it strikes his fancy. For the most part, he seems perfectly content to simply remain in his estate in the swamps of Toonol with a few servants to assist him in his studies and be left alone by the outside world.
To his credit, he accepts Vad Varo's condition that he use his abilities for the better of Barsoom and its inhabitants, and takes his promise sufficiently seriously to unhesitatingly agree to go with John Carter to the aid of a badly injured Dejah Thoris. The fact that he is being held prisoner by his hormad creations probably has something to do with it as well. The disastrous failure of his attempts to create life abashes Ras Thavas and glimmers of humility manifest themselves for the first time.
Ras Thavas would be the first to tell you he is a genius, probably the greatest mind in the solar system. He has perfected techniques for transplanting limbs and organs, including the brain, as well as preserving and reviving the dead. His attempt to create life however, goes horribly wrong teaching him his limitations.