Need SciFi book title: kidnapped human (hitman), Neanderthal [duplicate]

Question

Juvenile Sci-Fi novel, at least 30 years old, trying to resurrect based on a fond memory.

An Earthman, hitman I believe, is captured by an alien. The hitman sneaks "tapes" for machine based learning (card playing, martial arts, operation of alien machines eg Mark V hovercar?), outsmarting the unsuspecting alien while becoming incredibly intelligent.

He then goes to the stars and some mayhem ensues. Ending involves him determining that his "helper" is a previously kindapped (Neanderthal) Earthling, finding out that he had unknowingly split his intelligence into two halves, and reuniting both halves of his intellect.

Any ideas? Google was not helpful despite numerous attempts. Thanks!

Answer 1

Sounds a lot like a Keith Laumer novel The Ultimax Man. I remember the part about a mental being that helps the protagonist out being a neandrathal kept around for thousands of years.

A review from GoodReads:

*Minor hoodlum Damocles Montgomerie, whisked from the path of a speeding bullet to a concealed alien research center at the North Pole, achieves untold powers of cerebration in the course of having his brain picked by the donnish Xorialle. Once in command of his new abilities, Dammy promptly commandeers Xorialle's ship & sets out to track down the "Galactic Concensus" in the neighborhood of Deneb. The closer he gets, the more bewildering his discoveries about the origin of the whole adventure--the most curious pieces of the puzzle being a mild-mannered, bee-like creature by the name of Floss & a telepathic protohominid called Sport. *