The Olog-hai had been bred by Sauron from lesser Troll stock and had until the late third age been a rare breed. Cunning and organized - yet as big and strong as their lesser brethren - the Olog-hai were superb warriors. They knew no fear and thirsted for blood and victory.
The Olog-hai were also called Black Trolls, for they had scaly hides which were as black as their Torog blood. They were the smartest, and most dangerous of all the Troll breeds. These cunning and dangerous Trolls served as Sauron's elite troops. Standing 9 to 11 feet in height and utterly ruthless, they made superb commanders for the Dark Lord's Orc armies.
Able to bear sunlight easily and as intelligent as many Men, the Olog-hai were flexible, reasoning creatures. They spoke the Black Speech fluently and some knew Westron and other common tongues. Most could write. They always wore armor and used weapons. Most carried blank shields and war hammers, although they were adept at using almost any weapon. The Olog-hai also had a certain esprit d'corps, for unlike Orcs and lesser Trolls they rarely quarreled among themselves. Instead, they released pent-up anger by bullying lesser creatures, especially lesser Trolls, to whom they considered themselves much superior - as indeed they were.
The exact origin of the Olog-hai remained a mystery. It had been speculated that they were not Trolls, but rather, giant Orcs, but this seemed unlikely due to their distinctively Trollish anatomy. It's been speculated that perhaps Olog-Hai were either improved Hill Trolls or Mountain Trolls, or that they were the results of breeding such Trolls with something else, perhaps Uruk-hai, Half-Trolls, Demon-Trolls, Boldogs, men, or Giants.
- LOTRO has Olog-Hai and a Troll-Race very similar to them the Gortorogs. Gortorog may be translated as "Horrible Troll". Since true Olog-Hai did not appear until the late Third Age, about the same time as the Uruk-Hai, it may be possible that the early Ologs mentioned in the MERP canon were not yet true Olog-Hai but only Gortorogs, their earliest predecessors. Sauron seems to have needed over one and a half millennia for finally finishing his Olog-Hai, one of his earliest efforts ,the Troll Rugrul ,was born around TA 1600 and yet unimmunized to sunlight.
- In Shadows of Mordor it is implied that Sauron bred the Olog-Hai from magical Experiments with Trolls and the Graugs, a race of giant Troll-kind native to Mordor.
- Retrieved from [Realms of Arda]; original reference: [ICE MERP 2012],[ICE MERP 2000],[ICE MERP 8004]