Actor Vin Diesel plays Groot in the Marvel Cinematic Universe. 1 / 7
He recently penned a tribute to Iron Man actor Robert Downey Jr. 2 / 7
In an Instagram post, Diesel praised the actor's attitude and spirit. 3 / 7
He says Downey Jr. also expressed his confidence in the upcoming Fast & Furious 9. 4 / 7
Diesel also shared a picture of the two men together. 5 / 7
Fast & Furious 9 releases in 2020. 6 / 7
Avengers: Endgame is in theaters now. 7 / 7