Man Plus Series by Frederik Pohl, Thomas T. Thomas

Ill luck made Roger Torraway the subject of the Man Plus Programme, but it was deliberate biological engineering which turned him into a monster -- a machine perfectly adapted to survive on Mars. For according to computer predictions, Mars is humankind's only alternative to extinction. But beneath his monstrous exterior, Torraway still carries a man's capacity for suffering.

The events chronicled in the award-winning Man Plus were only the beginning. It is 50 years later. Man is on Mars to stay. But things have become strange, even compared to the population of cyborgs and human misfits who now occupy the Red Planet. The computer net on which all Martian life depends seems to have a mind of its own--and it's in a bad mood.