While much attention will be paid to the performances of Chris Pratt, Vin Diesel, Bradley Cooper and Zoe Saldana in Marvel's Guardians of the Galaxy, director James Gunn reveals the film will owe much to the work of one actor: his brother Sean Gunn.

Perhaps best known for his turn as Kirk Gleason on Gilmore Girls, the actor donned a body suit to play what turns out to be a few roles.

"Working with my brother Sean Gunn on Guardians of the Galaxy," James Gunn wrote last night on his Facebook page. "This photo [above] is from Sci-Fi magazine, which features a great article on how we work together and what Sean contributed to the character of Rocket and to the movie as a whole. It also reveals that, in addition to being the onset Rocket, and using a lot of his body and facial work in the character, he was also the onset Thanos, as well as playing the role of Kraglin, Yondu Udonta's First Mate in the Ravagers and Peter Quill's lifelong frenemy. Few things in my career give me more creative pleasure than working with my brother."

Asked in the comments why the film didn't use "a short actor" to play Rocket Raccoon, Gunn replied, "We also had a little person, who we used for reference and lighting in scenes -- the very very awesome Arti Shah," Gunn wrote. "But Sean is VERY limber and able to crawl around on all fours at the proper height (Rocket is actually smaller than almost all little people). But what was really important was Sean's acting. He essentially co-created the character of Rocket, and his acting is used throughout the film. It was also of great benefit to the other actors, who had a full scene partner who was as an accomplished actor as all of them. If you read the Sci-Fi article you'll find out from Zoe Saldana how important Sean was to the whole process and her personally. And I know Chris Pratt and Dave Bautista also agree. Bautista and Sean had -- and continue to have - a special bond that I think is very reflective of the onscreen bond between Rocket and Drax."

He also revealed that "a great Polish fellow by the name of Christian" played Groot on-set, but they didn't use his acting for the CG version of the character.

Guardians of the Galaxy opens Aug. 1.