Gus Van Sant on casting Joaquin Phoenix as a disabled person and carrying out Robin Williams' vision

Director Gus Van Sant is best known for his films Good Will Hunting, Milk and Finding Forrester, but he's also earned cult followings with his more experimental films like My Own Private Idaho and Elephant.

His latest film is a biopic called Don't Worry, He Won't Get Far on Foot​, which is based on the true story of cartoonist John Callahan, played by Joaquin Phoenix. Van Sant tells q guest host Talia Schlanger that the film is "something in between" the blockbusters and cult classics he's made before. 

John Callahan pretty much was just almost falling out of his chair with excitement that Robin Williams was going to portray him in a movie about his life. He thought that was the greatest thing that could ever happen.- Gus Van Sant

Don't Worry, He Won't Get Far on Foot​ depicts a difficult chapter of Callahan's life, when he was recovering from alcoholism and discovering his talents as a cartoonist after a car accident left him permanently paralyzed.

The role was originally meant to be played by the late Robin Williams, and while that never happened, Williams still ended up playing a big part in getting this film off the ground. Back in 1997, Williams had optioned the book by Callahan and told Van Sant about the cartoonist's story while they were working together on Good Will Hunting. 

The reason why Williams may have been drawn to Callahan's story, according to Van Sant, was because he was a close friend of Christopher Reeve, who became a quadriplegic in 1995. "It was a way for [Robin Williams] to maybe play a character that was in honour of Christopher Reeve. Also, it was about a cartoonist and a punster and a comic, which all kind of made sense to Robin."

Recently, some critics have questioned whether Phoenix, who replaced Williams and is non-disabled, should play the role of Callahan, but Van Sant says he "never thought in those terms" when it came to casting the part.

"I'm always interested in casting everyone as their real identity. It's amazing when you do that. ... I guess because it started with Robin Williams, we never really left that kind of idea. … [John Callahan] pretty much was just almost falling out of his chair with excitement that Robin Williams was going to portray him in a movie about his life. He thought that was the greatest thing that could ever happen."

Callahan died in 2010 and Williams in 2014, but Van Sant remained committed to carrying out the vision that they had created more than 20 years ago.

"It was still very clear in my head, John's life," says Van Sant. "And although it was sad that he was gone, and it was sad that Robin was gone as well. ... It wasn't like a dark cloud over the project for me."

Don't Worry, He Won't Get Far on Foot​ hits theatres on Friday, July 20.

— Produced by Beza Seife