Owner of the greatest celebrity Facebook page of all-time, Vin Diesel, is voicing the large tree-man Groot in the upcoming Guardians of the Galaxy. Groot is notable for only being able to say "I am Groot" - sort of like an outer-space Hodor with sliiiiightly greater knowledge of grammar and semantics. And so that the production wouldn't be forced to bring in other actors to voice the character for foreign markets, Vin Diesel opted to record the foreign language lines himself.
Not only does he go the extra mile by doing this (which is definitely NOT common practice in Hollywood), but he also wore stilts so that he would stay in character. It's pretty great.