Orion Series by Ben Bova

John O'Ryan is not a god...not exactly. He is an eternal warrior destined to combat the Dark Lord through all time for dominion of the Earth. Follow him, servant of a great race, as he battles his enemy down the halls of time, from the caves of our ancestors to the final confrontation under the hammer of nuclear annihilation.

The immortal being who has become the champion of humankind must struggle to find the woman he loves in the mystical world of the Great Hunter.

A sequel to "Orion" and "Vengeance of Orion". At the end of the Cretaceous Period, Earth is in the grip of the dinosaurs. Their leader is a reptile, worshipped by the Egyptians as a powerful god for thousands of years. His mission is to destroy the Creators - Orion's masters - and rule the planet.

John O'Ryan is Orion--more than human, less than a god, cast away on the seas of Time to do battle among the Creators for the future of mankind.Now the eternal warrior finds himself separated from his great love, Anya, and marooned in Macedonia under the reign of Phillip--fighting alongside the young Alexander, and at the mercy of a Queen Olympias who is far more than she seems.

A new installment in the military science-fiction series by a Hugo Award-winner finds the superhuman, outer-space warrior John O'Ryan caught in the middle of a dangerous contest between a goddess and a god. Reprint. K. VY.