The Olog-hai were a race of trolls bred by Sauron in the later years of the Third Age. They were first seen among the trees of Mirkwood, and the southern borders of Mordor. They were described as being taller than a man, covered in horny scales, and they carried hammers and bucklers in their claws.

They were superior to other trolls in almost every way. These were strong, agile, fierce and cunning, and they could endure sunlight - for a while, and if their Master's thought was with them. Many Olog-hai fought in the War of the Ring and in the Battle of the Pelennor Fields though most were slain during the Battle of the Black Gate.
Encyclopedia entry originally written by atalante_star