What was corrupted to create
trolls?
There is no evidence they are corrupted
Ents.
(But then again, there is no evidence at all.)
The Ents (or at least some) ARE said to have 'smooth gray skinned arms' in one place...
Though I don't know how Ents would be mixed with
other races, but hey... this is fantasy.
And
Orcs, twisted
Elves, are far 'lesser' than a true
elf... corruptions usually don't match up to the originals. (though there are exceptions, of course...like
dragons.)
So who knows. The product of ents they may be. Lesser...far dumber... weaker... much shorter (probably as whatever they were crossed with wasn't 12-14 feet high).
Or somehow a biological mixing of larger, stupider
races with
dwarves, and nurturing them until they're 'bigger than dwarves' and dumber than posts... nurturing as
Sauron did with the
Nazgul's
fell beasts and the biggest, smartest
trolls, the Olag-hai of the 3rd age. We have no clue what the fell beasts were originally either. Maybe twisted
great eagles, who knows.
Perhaps our lore masters have dug something out of the ever-effusive 'other
materials' version 19z or something...
THANKS for asking a question I've puzzled over for some time now... (heading to the aspirin bottle.)
We do have this:
"
Half-trolls was a term used to describe the appearance of the
men from
Far Harad who fought for
Sauron at the
Battle of the Pelennor Fields. These
Men were said to be black skinned with white eyes and red tongues.
[1] Later in the battle, the knights of
Dol Amroth were said to have driven before them "troll-men and Variags and orcs."
[2]"
That contains some hint of cross-breeding.
Biological tampering seems to be a great focus of the darkness. Rejecting what "is", corrupting what "is", trying to transform it into something 'better'.
'Better' however is defined as 'more suitable to the purposes "I" want'. It doesn't mean they're really any 'better'. The Agenda drives the evaluation and conclusion.