He is Groot — and apparently, he is awesome.

Over the weekend, Guardians of the Galaxy director James Gunn wrote a lengthy Facebook post about working with Vin Diesel, who supplies the voice for Groot, the sentient tree-creature who can only say the words "I am Groot." From the sound of it, Gunn is pleased with how those three crucial words came out:

Vin Diesel just finished his final session as Groot (well, for 2014 at least). All of us are astounded that one man can bring so much amazingness to a character who can only say three words. We don't affect Vin's voice at all and he sounds like an otherworldly tree! Every "I am Groot," every grunt and shriek and whine and holler is filled with heart and humor and passion. When I returned from the session, I told one of our producers, Victoria Alonso, that I think we could audition every single person in the world for Groot, and Vin Diesel would still be the best. I know directors almost always praise their stars - and, God knows, I've been fortunate with the entire cast of Guardians of the Galaxy - but I've never been more stunned by an actor able to bring so much more to a role than I originally thought possible. Rocket may be the heart of GotG, but Groot is its soul.

Opening Aug. 1, Marvel's Guardians of the Galaxy also stars Chris Pratt, Zoe Saldana, Bradley Cooper, Dave Bautista, Djimon Hounsou, Michael Rooker, Karen Gillan, Benicio Del Toro, Josh Brolin, Glenn Close and John C. Reilly.