Xenu

None of you could possibly'' understand. ''

Xenu is-- if one L. Ron Hubbard is to be believed-- the long-deposed leader of the Galactic Confederacy whose soul (or "thetan") was presumed lost on Earth. Xenu is now-- if one Dr. William Newman is to be believed-- the powerful force animating him and granting him awe-inspiring powers to achieve some unknown end, possibly his own corporeal resurrection.

Dr. Newman was killed by The Guardians of O.R.D.E.R. on board the Odyssey, separating him via teleportation as he attempted to combine his matter and energy powers (in two separate bodies) to make an even more powerful explosion than the thermonuclear bomb So-Lar disabled.

Skills and Powers
Xenu possesses mastery of what he calls "MEST"-- Matter, Energy, Space, and Time. He seems to prefer using one of these powers at a time (as the first time he fought with the Guardians, he used only matter control to attack and defend). The full extent of his powers is unknown, but assumed to be vast-- after all, he can somehow coat the walls and doors of every room on the cruise ship Odyssey with portals that stretch through boundless space to prevent anything from passing between them.

William Newman himself is not known to have any powers.

Backstory
William Newman's backstory is to some degree public knowledge. He was born in Albany, New York and moved to New York City to attend college, graduating with a Doctorate of Psychology at the relatively young age of 27. He came from a wealthy family and cultivated his money into a successful practice acting as a therapist for the rich and famous. He met several Scientologists during this time, and it was on vacation with some in Cyprus that he nearly drowned. Against all odds he arose from the Mediterranean Sea alive after four hours, a shaken but otherwise unchanged man. That was, until, he began developing unusual powers....

He left his practice at the age of 31 (in 1994) and became a full-time devotee of Scientology, serving as a recruiter and rising in rank, ascending in Operational Thetan levels unseen due to his powers, which were kept a secret between he and leading members of the group. A successful and charismatic man, Newman became the most prominent "face" in the organization and began to influence its direction. The cruise on board the Odyssey seems to be the culmination of his plans, whatever they might be.

The knowledge of the source of his powers died with him: when Newman was drowning off the coast of Italy, he fell into the Marsili underwater volcano, in which he found the source of its geologic instability... the shattered debris of a spaceship, little remaining but a magnetically sealed box. A panicked Newman touched it, when "awakened" and bestowed him his powers, instantly saving his life (as he could transform the water into air). He believed it to be the wreckage of Xenu's ship, as it looked vaguely like an airplane and Scientology lore suggested Xenu was sealed on "Teegeeack" (or Earth) anyway. He came to believe that he could use "Xenu's" powers to fulfill the destiny he felt he was promised.

Miscellanous Trivia

 * Unlike many Scientologists, Dr. Newman has no special animus against psychologists or psychiatrists, and discourages his colleagues from disparaging either profession.
 * He is unironically a big fan of Seinfeld, although there is one joke he gets tired of hearing....
 * Newman is rabidly anti-military. It's not known whether this is a political opinion, or a viewpoint that changed since he became "Xenu" (as Scientology lore suggests Xenu was deposed by his military); he still wears a military uniform under his high-tech armor in Xenu form.