The 'Bourne Identity' actor and friend Ben Affleck launched their careers with 1997 movie 'Good Will Hunting' - which they wrote and starred in - and he doesn't think he would have enjoyed the life he has since then if the late actor hadn't agreed to take on a starring role.
He said: "Ben (Affleck) and I owe everything to him. He said yes to our movie and he got it made. I could never thank him enough. I look around at the life I have and how blessed I feel and so much of it started with him."
The 43-year-old actor was "shocked" when Robin, 63, committed suicide last month and hopes the tragedy will raise awareness of depression and how debilitating it can be.
Speaking to Yahoo! News' Katie Couric, he said: "I was shocked. I hadn't been in touch with him and obviously, he was battling severe depression and I hope it can start a conversation in the country about depression, just how serious it is and what an exceptionally powerful disease that it is.
"I think it affected everybody in the country actually. We all felt like we knew him and he was a part of our lives."
Matt went on to praise the 'Mrs. Doubtfire' star as the "funniest person" he ever met who could always lift the spirits of those around him.
He said: "He was the funniest person I ever met in my life. He was the guy who, when the crew was flagging, would stop everything and do 20 minutes of stand-up off the top of his head that literally had everybody on the floor and we were like, 'Ok, let's get back to work'.
"He was amazingly generous with that time he gave to help other people but just in life, if you walked down the street and if somebody stopped him he would talk to that person, he engaged with every single person and he understood at some level, the impact that he had on people. He could see people light up when they saw him.
"I think that is what I carry with me... the joy he brought in my life."