Mark Ruffalo has hailed Robert Redford as a "real American hero"

Mark - who worked with the acclaimed actor on the 2001 movie The Last Castle - captioned his Instagram post: "This was a letter I had written to Robert Redford when I learned he was ill. I didn't get it to him before the news today. This is what a real American Hero looks like. A man who brought people together, lived and practiced empathy, and created good and useful organizations that made peoples lives better and included anyone who had an interest. Please remember him well. (sic)"

In his letter, Mark reveals that he staged a reading of Redford's 1976 movie All the President's Men, while he also shared memories of working with the acclaimed film star.

Part of the letter reads: "You have had the most profound impact on my life and career in so many ways. You have been a hero of mine.

"I told you before. The short time together we had on The Last Castle was seminal to me. To be acting opposite of you. To have you be so generous with me. I felt so safe with you and looked after."

Elsewhere, Leonardo DiCaprio has also paid a heartfelt tribute to Redford.

The 50-year-old movie star described the actor as a "champion of the arts".

He wrote on Instagram: "Actor, activist, passionate environmentalist, and champion of the arts. His unwavering commitment to protecting our planet and inspiring change matched his immense talent. His impact will endure for generations to come."

Redford passed away on Tuesday at his home in Utah.

A statement read: "Robert Redford passed away on September 16, 2025, at his home at Sundance in the mountains of Utah - the place he loved, surrounded by those he loved. He will be missed greatly. The family requests privacy."