Rich had worked as the Iron Man star’s personal assistant since 2003, and became close friends with many of the Avengers cast and crew and their families.
On his Instagram, Downey Jr said that Rich was killed in “a fatal car accident” on Wednesday (5 May), and credited him with supporting his sobriety.
“This is a terrible and shocking tragedy,” the actor wrote. “He was a brother, my right hand man, an uncle to our kids and beloved by all who experienced his singular character and wit... our thoughts go to his relatives, friends, co-workers, and all the fans who knew him as the man who supported every step of my recovery, life and career.”
A number of Downey Jr’s Marvel co-stars also left tributes.
Chris Evans posted a picture of himself on an Avengers set posing with Rich, and captioned it: “I don’t have the words. Jimmy Rich was unlike anyone else. He left an indelible impression on everyone he met. No one more so than my brother @robertdowneyjr They were inseparable.”
Evans continued: “I’m sending all my love to Jimmy’s friends and family. Be sure to hug your loved ones tightly and please take the time today to show Downey how many people love him and are here for him during this incredibly dark time.”
“Such a tragedy,” wrote Mark Ruffalo in Downey Jr’s Instagram comments. “Such a good man. I have known him almost as long as I have known you, Robert. Breaks my heart to have Jimmy go over to the other world. You will be missed Jimmy. Thanks for always being real, always being there to lend a hand and showing the way of light forward to so many people. Another sad day.”
Gwyneth Paltrow commented “Please no oh my god”, while Chris Hemsworth wrote that he was “heartbroken”. Josh Brolin wrote that he has “no words, just tears and gratitude for the gift that was him”, and Jeremy Renner called Rich’s death “a devastating loss”.
Chris Pratt added: “That sucks so bad. I’m so sorry to hear that. He was awesome. Such a tragedy.”
Rich had worked with Downey Jr since the actor became sober in 2003 following years of drug addiction. Rich himself had battled addiction, writing in his Instagram bio that he had been “clean and sober” since December 1998.