As Robert Downey Jr. celebrated his 55th birthday this weekend in Los Angeles, the social media highways and biways flooded with well wishes and warm sentiments from many of his MCU co-stars - including Chris Evans, Mark Ruffalo, Jeremy Renner, and Gwyneth Paltrow. Marvel's Black Widow may have been delayed until November, taking The Eternals' premiere date, but the Avengers aren't about to skip a chance to assemble.