The Olog-hai were a fierce race of Trolls. They only spoke Sauron's Black Speech, and it is possible they only existed because Sauron's evil will empowered them. They were bred by Sauron from an unknown stock, though it's suggested that they could be corruptions of some primitive human types.
During the War of the Ring, Sauron used Olog-hai in the Siege of Gondor and Battle of the Pelennor Fields. In the subsequent Battle of the Morannon, the hobbit Peregrin Took killed a large Olog. As a result of Sauron's ring being destroyed, the Black Gate and the rest of Mordor collapsed to ruin during that battle. Most of the Trolls present at the battle were killed, with a very few escaping.
The Olog-hai had none of the old Troll vulnerabilities: they were very intelligent and able to endure the Sun. For this reason they were seen by some to be giant Orcs (though surpassing even the Uruk-hai in size and power), but they were definitely of Troll stock.
The Olog-hai that fought in the War were described as being taller than a man, and covered in horny scales, carrying hammers and bucklers in their claws.[source?]
 Portrayal in Adaptations
1982-97: Middle-earth Role Playing:
- Olog-hai, also called Black Trolls, were bred by Sauron from lesser Troll stock. They are nine to eleven feet in height, and have black, scaly hides. They appear much earlier in history than Tolkien indicated, as early as the wars with Angmar. Individual Olog-hai include the warlord Rogrog of Angmar, Umagaur and Lugronk.
- Olog-hai were shown as the shock troops in the Siege of Gondor, sporting armor and the famed war hammers alluded to in the appendices. These Olog-hai were not shown talking in any speech other than grunts. They differ from the other Trolls depicted in Peter Jackson's The Lord of the Rings in that they have more forward-facing eyes as well as hair on their bodies, suggesting that they are a more advanced form of Troll. They are usually gray to black in color. They have twenty-four teeth. Their eyes are also bright orange, showing their evil connection with Sauron.
- ↑ 1.0 1.1 J.R.R. Tolkien, The Lord of the Rings, Appendix F, "The Languages and Peoples of the Third Age", "Of Other Races"
- ↑ J.R.R. Tolkien, Christopher Tolkien (ed.), Morgoth's Ring, "Part Five. Myths Transformed", "[Text] IX"
- ↑ J.R.R. Tolkien, "Words, Phrases and Passages in Various Tongues in The Lord of the Rings", in Parma Eldalamberon XVII (edited by Christopher Gilson), p. 136
- ↑ Helge Fauskanger, "Orkish and the Black Speech" , Ardalambion (accessed 13 March 2014)
- ↑ R. Mark Colburn, Peter C. Fenlon, John D. Ruemmler, Terry K. Amthor, Jessica M. Ney (1989), Lords of Middle-earth Vol III: Hobbits, Dwarves, Ents, Orcs & Trolls (#8004)
- ↑ S. Coleman Charlton (1993), Middle-earth Role Playing (2nd edition, hardcover) (#2000)
- ↑ Ruth Sochard Pitt, Jeff O'Hare, Peter C. Fenlon, Jr. (1994), Creatures of Middle-earth (2nd edition) (#2012)
- ↑ Graham Staplehurst, Heike Kubasch (1995), Angmar (2nd edition) (#2018)
- ↑ 9.0 9.1 Peter C. Fenlon, Jr. (1994), Moria (2nd edition) (#2011)