Robert Downey Jr Celebrates His 56th Birthday, Marvel Co-stars Send Their Love — See Messages

"Iron Man" star Robert Downey Jr. celebrated his 56th birthday on Easter Sunday, and his "Avengers" co-stars took turns to honor him with heartwarming messages.

Robert Downey Jr. is famous for his portrayal of Iron Man in the Marvel Cinematic Universe. Hence, when he celebrated his 56th birthday on Easter Sunday, it was not surprising to see him overwhelmed with messages from friends and fans worldwide.

Leading the messages were Downey Jr.'s Marvel co-stars, who took turns to celebrate him with multiple heartwarming messages and tributes.

Mark Ruffalo, who portrayed Hulk and Dr. Bruce Banner in Marvel's "Avengers," shared a picture of himself and Downey Jr. In the post's caption, Ruffalo wished his co-star and the other half of the #ScienceBros a happy birthday.

Jeremy Renner, who portrayed Clint Barton and Hawkeye in "Avengers," also shared a picture of himself and Downey Jr. and, in his caption, wrote:

"Happy birthday to my dear friend @robertdowneyjr Happy Easter to you. Bestowing loads of love and laughter with family and friends today my brother."

Chris Hemsworth, who portrayed Thor in the "Avengers" and "Thor" movie series, shared three pictures of himself and Downey Jr. showing their goofiness.

Paltrow said she was able to find an incredible, lifelong, inspirational partner and friend in Downey Jr.

In his caption to the post, Hemsworth wished his co-star and friend a happy birthday and described him as a special human. He hailed Downey Jr.'s mind-blowing creativity and unrivaled leadership.

Hemsworth said this helped them to ride on the latter's coattails through the Marvel Cinematic Universe. Hemsworth concluded by expressing his eternal gratitude to Downey Jr.

He added that he loves him. Downey Jr. was overwhelmed with love shown to him by his co-stars and fans worldwide and took to his Instagram page to express his gratitude, saying:

"Much love and gratitude for all of the birthday well wishes! Many reasons to feel blessed today. #HappyEaster #HappyPassover #BirthdayDowneyJr."

During his time in the MCU, Downey Jr. built a lifelong friendship with actress Gwyneth Paltrow, who portrayed Pepper Potts, Iron man's assistant, and future wife.

In a chat with People, Paltrow said she was able to find an incredible, lifelong, inspirational partner and friend in Downey Jr. Besides his exceptional Hollywood career and great friends, there are many more things Downey Jr. has to celebrate on his 56th birthday.

Chief among these are his three children, who are his heart and soul. The actor's kids include his oldest son, Indio, who he welcomed in 1993, and shares with his first wife, Deborah Falconer.

After divorcing Falconer ins 2004, he married Susan Downey in 2005. With her, he shares his second son, Exton, who was born in 2012, and his daughter, Avri, who they welcomed in 2014.