Downey, on Sunday, described how Marvel's Iron Man helped with his career resurgence following a dark period in his life.
"I hate to say this, it's a very American thing you know to build up and break down and come back. It is in it's own weird way, it is the hero's journey," Downey said in reference to his return to Hollywood.
"I could relate to Tony Stark a lot by the time I played him. A guy who needed to really be handed a dose of ouch," the actor continued.
Downey also discussed how much he enjoyed portraying Tony Stark/Iron Man across multiple films leading up to Avengers: Endgame.
"The greatest thing for me as a fellow, I love this stuff. I geek out over it. I got to experience it by playing it you know and it was just unforgettable," Downey said.
Colbert was hosting a special installment of The Late Show, which took place following Super Bowl LV. Tiffany Haddish also appeared with Metallica as the musical guest.
Metallica performed their hit "Enter Sandman" inside a warehouse. The band was surrounded by speaker cabinets from various Metallica tours and special performances.