The Olog-hai were a race of Trolls that appeared at the end of the Third Age, in the south of Mirkwood and in the mountain borders of Mordor. Tolkien describes them in the appendix on the languages and peoples of the age, and nowhere else in the published story are they named.1
Treebeard called Trolls mere counterfeits, made by the Enemy in the Great Darkness in mockery of Ents, and the appendix agrees that the old Trolls were dull and brutish creatures that could not bear the sun.2,1
But the Olog-hai were bred by Sauron, and they were a new kind: strong, agile, fierce and cunning, and, while Sauron's will held them, able to endure the sun.1
They spoke little and knew no tongue but the Black Speech of Barad-dûr. That Sauron bred them none doubted, the appendix says, though from what stock was not known.1
A great company of hill-trolls out of Gorgoroth fought in the army of Mordor at the Battle of the Morannon, before the Black Gate. Pippin, fighting beside the men of Gondor, slew the troll-chief that had struck Beregond down, and was buried beneath it as it fell.3
Interpretation The text does not name the trolls at the Black Gate as Olog-hai, but hill-trolls fighting in the field by day, in Sauron's own army, fit the appendix's account of them closely.3,1
Sources
Citations name the chapter rather than the page, so they work in any edition. The colour of each note shows what kind of source it is.
- Published story The Hobbit and The Lord of the Rings as Tolkien published them.
- Appendices Tolkien's own appendices to The Lord of the Rings.
- Appendices The Lord of the Rings, Appendix F, I, “The Languages and Peoples of the Third Age”
- Published story The Two Towers, Book III, ch. 4, “Treebeard”
- Published story The Return of the King, Book V, ch. 10, “The Black Gate Opens”