The upcoming forth sequel of the "Iron Man" movie franchise is scheduled to open in theaters in 2020, yet rumors already spread that Robert Downey Jr. will not play the iconic role.

In this fourth movie series, it is widely speculated that Tony Stark will be replaced by Riri Williams - a 15-year old engineering savant recently added in the Marvel universe as Stark's eponymous successor.

The production for "Iron Man 4" is already set, but the main casting remains to be concluded. Several possible theories contribute to the possibility of Robert Downey Jr. refusing the future reprisal.

There are some assumptions that point to a lack of mutual consensus between Downey Jr. and the producer in terms of salary. This conjecture is firmly supported by News Everyday in their recent article. Marvel Studios president, Kevin Feige, confirmed that future characters will be represented by new actors.

An alternative speculation regarding the future "Iron Man" role replacing Downey Jr. also points to his age and overall condition. As reported by Game N Guide, Robert Downey Jr. is too old to portray Tony Stark by the time "Iron Man 4" is released.

Several other Marvel films are lined up before "Iron Man 4". These titles include "Avengers: Infinity War" (parts 1 and 2 consecutively) slated for 2018 and 2019 respectively, as well as "Spiderman: Homecoming".

Certainly, the issue regarding Iron Man 4 is still far from the concerns of Robert Downey Jr. since he's currently busy with the third "Sherlock Holmes" movie trilogy. The depiction of the classical 19th Century private investigator of Victorian England was one of the two most enduring roles of his acting career. 

Despite the much-awaited return of Tony Stark's "Iron Man 4", fans will have to wait a little longer for any solid confirmation. Until then, Robert Downey Jr. remains as billionaire philanthropist playboy in the prior upcoming Marvel films.