"In their beginning far back in the twilight of the Elder Days, these were creatures of dull and lumpish nature and had no more language than beasts" it goes on to say that Sauron used what little intelligence they had to teach them rudimentary speech and nuture the clever and dark nature within in them. It also states how in time the Olog-Hai (High Trolls) were brought forth by his actions.

"Trolls they were, but filled with the evil will of their master: a fell race, strong, agile, fierce and cunning, but harder then stone." they could also endure to the light of day so long as Sauron held sway over them.

So the troll as all the servants of evil was a twisted mockery of what it once was.