I imagine a huge greenish/brown guy with arms like tree trunks. He did say trolls were an abomination make to mock Ents, so they should look kinda troll like. Kinda like that troll in Harry Potter, but a bit more tree looking and a bigger head (and thus bigger brain). Both frightening and friendly at the same time... boy this is long winded, isn't it??? Just really big and very earthy looking. (of course, I skipped a lot of description in the book...) And his voice I think RysDavies could do well... I imagine a kinda thoughtful, raspy voice.. sometimes clear, but most of the time sounding like he's talking to himself.