Robert Downey Jr.'s contract to continue playing Tony Stark aka Iron Man ends with the currently untitled "Avengers 4." However, as reported by MNR Daily, it is possible the films will take a cue from the current Marvel comic books and Stark will pass the mantle of Iron Man to Riri Williams aka Ironheart.

In the comic book source materials, Tony Stark decided to finally retire as Iron Man following the events of "Marvel Civil War 2." It was during this time he met Riri Williams, a young female African-American teenager who was also a genius and had been able to design her own suit from scrap. 

Comic book writer Brian Michael Bendis explained in an interview with Wired that even though Riri is the one in the suit her AI companion has been programmed to be similar to the personality of Tony Stark, ensuing his presence is always around even when Stark is physically somewhere else.

In regards to the nam Ironheart, Bends explained that it came about during a group discussion with his editors for the "Invincible Iron Man" series.

"Iron Woman seemed old-fashioned to some. Iron Maiden looked like a legal nightmare. And Ironheart, coined by Joe Quesada, after I told him my planned story for Riri, speaks not only to the soul of the character but to the Iron Man franchise as a whole," he stated.

As pointed out by Parent Herald, Downey Jr.'s talent fee continues to rise and it may be due to financial reasons that Marvel Studios will no longer sign him on for future Marvel Cinematic Universe movies. Because of this Stark may pass the baton to Riri Williams by "Avengers 4" or in the beginning of "Iron Man 4."

Marvel Studios have yet to announce "Iron Man 4" and whether or not Downey Jr. will be reprising the role or if the films will be adapting the story arc of Riri Williams.