Batman's main enemy has been masterfully played by Jack Nicholson ("Batman", 1989) and Australian Heath Ledger ("The Dark Knight", 2008), but the star's performance of "Gladiator" is possibly the most radical. so far.
His performance was described as "sensational" and "disconcerting" by some critics, but others opined that his approach to mental illness and character violence could be "incendiary".
"There was something that attracted me to him and it evolved as we worked together," Phoenix told the Toronto audience after the film was screened alongside director Todd Phillips.
"It started to become something more than I could have anticipated and was one of the best experiences of my career," he said.
Phoenix also paid tribute to his late brother River Phoenix as he recalled how he led him to see "The Angry Bull" as a teenager and told him that he too would be an actor.
"He didn't ask me, he told me. And I'm indebted to him because acting gave me an amazing life," he said.
River Phoenix, who was initially more prominent than his younger brother and played the young Indiana Jones in "Indiana Jones and the Great Crusade" (1989), died at the age of 23, an unfortunate episode that ended with a recording sold to Joaquin's desperate phone call calling an ambulance.
Joaquin Phoenix was on the red carpet of the Canadian festival alongside Robert de Niro, who also enters "Joker".
Batman's production of the villain is set in the 1970s and is based on De Niro's own feature films such as "Taxi Driver" (1976) and "The King of Comedy" (1982), both by Martin Scorsese.
De Niro said he "understood all the calls," but made a point of highlighting that he joined the project because of director Todd Phillips.
'How did he do it?"
Phillips was best known for comedy movies, such as the "The Hangover" trilogy.
"I hate it when people come to me making a face like 'who did' The Hangover 'did it," "said the director.
The Toronto International Film Festival runs until September 15th. "Joker" arrives in Portuguese theaters on October 3rd.
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