Gharl, from Ultima VII
Gharl didn't reveal why exactly he was imprisoned, although it's possible that it was because of the normal way Trolls live, by plundering and killing other people. Gharl told the Avatar a little about the Troll way of life, but then revealed that he was starving because he gravely mistrusted the prison guard Goth. Offering Gharl some food, the Troll was thankful and revealed a secret: A strange voice helped the Trolls in Britannia.
The Avatar knew what that meant. The Guardian tried to control the Trolls of Britannia.