The most common and most likely answer to this crossword clue is the 9 letter word TORMENTOR
I've seen this crossword clue in The Guardian
T
O
R
M
E
N
T
O
R
More clues leading to the result TORMENTOR
- One persecuting people in the hills of Devon
- Mountain guide, one causing irritation
- One who harasses soldiers trapped between hills
- Rubbish about adviser being inflicter of suffering
- One persecutes soldiers surrounded by hills
- Scourge of people between rock and hard place
- Tremor not around one who bullies you
- He’s annoying hill guide
- Troll chaps found in Twin Peaks
- Bully fell upon teacher
Buddy explains!

The straight part
We know that "Troll" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case troll = tormentor.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.
What does TORMENTOR mean?
TORMENTOR noun- One who torments; a person, animal, or object that causes suffering.
- Something abstract that causes suffering.
- One of a pair of narrow curtains just behind the front curtain and teaser that mask the areas on the sides of the stage and can be adjusted to the desired width.
- An implement for reducing a stiff soil, resembling a harrow, but running upon wheels.
- A long meat-fork.