I read a book series 12 or so years ago, and I need help getting the title. It's set in the future. Mankind has branched out to the stars and many planets were colonized. Humans started to evolve differently on these planets. Now, I remember the main character as being a "spartan", and he grew up and was trained on an arid planet. His entire people were massacred and he was the only survivor. An advanced alien race took him in and augmented his bones to be unbreakable. I think that these aliens looked like owls, but I am not sure.
This is the Last Legionary series by Douglas Hill. The protagonist is Keill Randor a member of the Legion of Moros, a planetary culture whose primary export is mercenary skill and is recognized through the galaxy as the source of the best fighting forces.
Warning, light spoilers.
Keill is a champion among the Legion. He is off-planet when Moros is attacked and decimated by a force under control of an entity only known as the "Overlord". Keill received a lighter dose of the same process which killed the Legion, but condemning him to a slow death as his bones decay.
Under care of an alien presence opposed to the Warlord, Keill's skeleton is completely replaced with an infrangible substance (a la Wolverine's admantium) at once curing him and increasing his fighting effectiveness.
Keill's new mission is to help find and stop the Overlord. He is acommpanied on his journey by a telepathic alien companion named Glr