Well....Sauron did create the Uruk-hai....and maybe Sauron did some gene splicing between uruks, mountain trolls, and another troll like being....Perhaps in the Second Age, Sauron did capture some Entwives, and tortured them into some horrid being that resembeled a gnareled tree but with troll-like disposition. But waving off the wife part, then the Entish characteristics would reenter troll DNA (or whatever) to enhance brute strength, resiliance to the Sun that most trolls didnt have, and a more thick and hard skin/hide(like the bark of an Ent/tree). Coupled with the manuverability and intellegence from Uruks, the Olog-hai could then use and understand other melee weapons (besides club weapons, obviously excluding rang weapons), plus comprehend the need (and reason) for using a shield, and possibly light armor. Also, since Olog-hai appear to have some whiskers, so maybe some mannish strain was entered (for stubborness, the Sun resistance, etc), but maybe also a Half-Orc/Goblin Man like those Sauruman bred.
Of course, there is some speculation there, but its a rather interesting theory.

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2008 Cup