The HBO film, "A Father... A Son... Once Upon a Time in Hollywood," (search) premieres Saturday at 8 p.m. EDT.
Michael Douglas said he thought his father's best work came in the 1962 western "Lonely Are the Brave." (search) In that film, Kirk Douglas plays cowboy and ex-con Jack Burns, who rebels against modernity and is pursued by the law.
"It was a very different type of persona than Dad is normally known for," said Michael Douglas, 60. He said that when he and his wife, Catherine Zeta-Jones, ask their 2-year-old daughter Carys to "do Pappy," she mimics her grandfather's growls and facial expressions from the film.
Kirk Douglas, 88, chose a somewhat unusual role as his favorite performance of Michael's: the character in "Falling Down," (search) from 1993. In that film, Michael plays William Foster, an unemployed worker who loses control, goes on a rampage against society and is pursued by the law.
"I thought he was brilliant," Kirk Douglas said. "Whenever I see that picture, I don't see my son. I see that pathetic character."
The HBO documentary was directed by Lee Grant, the actress who won an Oscar for Best Supporting Actress in the 1975 Warren Beatty film "Shampoo."
Grant, 77, has directed dozens of documentaries for TV, and the HBO Web site says her "close friendship with Michael Douglas allowed her unfettered access to the two legends."