The Trolls have always had a single ruler, the Mountain King. After he was killed in the Battle of the Riven Mountain the Trolls' power waned, and they became divided. Two factions formed; one believed that none but the Mountain King ought to rule them, and the other believed that rule should pass to Deep Giant, the fosterling of the Mountain King.
Trolls are the caretakers of the Dreaming, and have a particular relationship with Oaths.
Trolls have been around almost from the beginning. The Kithless fae at the beginning became Nocker and Trolls when one of them made the Gate of Ivory. The Sluagh were created through the actions of the Trolls.