But at the end of the Third Age a troll-race not before seen
appeared in southern Mirkwood and in the mountain borders of
Mordor. Olog-hai they were called in the Black Speech. That
Sauron bred them none doubted, though from what stock was not
known. Some held that they were not Trolls but giant Orcs;
but the Olog-hai were in fashion of body and mind quite unlike
even the largest of Orc-kind, whom they far surpassed in size
and power. Trolls they were, but filled with the evil will
of their master: a fell race, strong, agile, fierce and
cunning, but harder than stone. Unlike the older race of the
Twilight they could endure the Sun.... They spoke little,
and the only tongue they knew was the Black Speech of Barad-dur.
[ The Return of the King, by J.R.R. Tolkien ]