The other half of the Guardians' dynamic duo is Groot, the walking, talking tree-man voiced by Vin Diesel. Diesel seems like a bit of a wasted casting choice for the part, considering Groot only ever says three words, "I Am Groot." We already know that Thanos has been cast, could Diesel be putting in some extra work to play the Mad Titan as well? Only time will tell. Groot, on the other hand, looks awesome, and you can bet that he'll be stealing quite a few scenes of his own. he appears to be a bit of a gentle giant when you're on his good side, lighting up a room with fireflies and giving a little girl a flower that he likely plucked from this own body. However, don't get on his bad side, becuase he looks like on hell of a fighter, getting a few Hulk smash moments of his own. And when that's not enough to get the job done, his best pal Rocket is glad to jump on his shoulders and rapidly fire away.