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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.