The Silver Brain
His real name is Sergei Vlataroff, and he was a scientist who found a way to permanently convert himself into "pure brain". In his converted state, he resembles a giant disembodied silver-colored brain.
Lacking a body, he often utilizes telepathically-controlled underlings. Typically, these thralls will build highly advanced machines under his guidance, which the Brain uses as part of his schemes. He is guarded by his Anti-Bodies, energy beings who serve as his last line of defense. On at least one occasion, he was aided by his Sledgehamsters, though whether they were mind-controlled thralls, robots, or something else is unknown.
In addition to his immense telepathic power and perfect memory, he is a scientific genius.
He attempts to build a neural-net which gives his psionic command of peoples brain in a certain proximity. He also needs the Dimensional Aperstomum, to help him remain in our dimension or risk being sucked back into the Mento-Verse.