STORY: Vin Diesel Stays Confusingly Cryptic on Marvel's 'Interesting' Plans

"What can I say about Groot? I can say something about Marvel," he tells The Hollywood Reporter. "I take my hat off to them for being so creative and thinking outside of the box."

Diesel says that he had originally met with Marvel to launch a fresh IP (intellectual property).

"That was the focus of our conversation — a fresh IP that would come out in 2016 or 2017, and potentially launch the third phase," he tells THR.

But then he went to Comic-Con to promote Riddick. At the annual convention in San Diego in July, he realized that fans didn't want to wait that long to see Diesel as part of the Marvel universe.

STORY: Bradley Cooper in Talks to Voice Rocket Raccoon in Marvel's 'Guardians of the Galaxy'

"With my schedule, it was almost impossible to imagine I could do anything immediate," says Diesel who will star in the upcoming seventh installment of the Fast & Furious franchise and has several other films in various stages of production.

"I guess after they watched Iron Giant, or whatever, they came up with this idea of taking the strangest Marvel character -- or the strangest Marvel character that's ever hit film -- and thought what I could do with that with motion capture and with my voice," he said.

Groot is an alien living tree that appeared various Marvel comics. A teaser shown at Comic-Con and Disney's D23 Expo showed that Groot will appear in James Gunn's upcoming pic. In the short teaser, Groot did not speak.

Adds Diesel: "Now it's just up to my reps to allow that to happen."

Guardians of the Galaxy, starring Chris Pratt and Zoe Saldana, is slated for release on Aug. 1, 2014.

Riddick opens in theaters on Sept. 6.

E-mail: Rebecca.Ford@thr.com

Twitter: @Beccamford