Last summer, Marvel announced that Robert Downey Jr. would return to the MCU, as an increasing number of rumors suggested. But he wouldn't play Iron Man, whose resurrection we expected for Avengers: Doomsday and Avengers: Secret Wars.
Instead, RDJ would play another iconic Marvel character we're dying to see in the MCU, Doctor Doom. He wouldn't be the main villain of the The Fantastic Four reboot. RDJ's Doom would replace Kang as the big multiversal villain that will start a new multiversal war.