Introducing viewers to the life and eclectic career of his father, 57-year-old Downey Jr jokes at one point in the film that Anderson was the son his father always wanted, noting that the two would always rub it in his face.
Addressing their coveted relationship in a new interview with Deadline, Downey Jr said: “Paul Thomas Anderson is as much a national and industry treasure as you could ever ask for.
“He’s found a way to have longevity in a way that eluded my father, and yet the fact that he took some small inspiration and developed such a paternal relationship with my dad.”
Continuing, Downey Jr acknowledged that “sure, I had my jealous moments, but I know where I stand, and I just respect and admire both those guys”.
“However, I am a little tad bit jealous of the laughs they had because I feel like those were two guys who were able to get to the root of each other’s funny in a way that is a rarity,” the Oscar-nominated actor added.
“I celebrate that in the film. I also just thought that it was a good line to say,” he explained of his earlier quip. “Sometimes in ‘Sr.’ I was just saying, ‘What’s the button we need here,’ or ‘What’s going to give them something to cut away to and how can I pass the baton to this great sequence of this film footage we have of them?’”
After thanking Anderson for “letting us include him in this story”, Downey Jr teased: “What can I do but take the knee to that guy?”
Anderson is best known for films including There Will Be Blood, Boogie Nights and Licorice Pizza.
Elsewhere in the interview, Downey Jr hit back at Quentin Tarantino’s earlier criticism of Marvel films, saying: “Creatively, it is a waste of time to be at war with ourselves.”
In a separate interview with The Independent, Smith spoke about the late Downey Sr’s reaction to his son’s Marvel success.
“I definitely think there were films that [Downey Sr] didn’t care for,” Smith said. “And I think, as Robert would openly admit, his dad wouldn’t hide his disdain if there was something he didn’t like.
“But, you know, when we asked him about the Marvel movies – about Iron Man in particular – I remember he loved it. He was like, ‘You have a guy who wants to give up his weapons!’ I think he was really proud, to be honest.”
“Sr.” is out on Netflix now.