The father was Hollywood's great seething masochist, enduring crucifixion, an eye-clawing, an ear-slicing, impalement on barbed wire and sundry brutal beatings, always with passions aflame and nostrils flared. The son belonged to a more ambivalent era on-screen: Here he's a heartless carnivore, there he's morally compromised, now he's befuddled, now he's the last angry man. Together they are one of the movies' great parent-child acts.

They're Kirk and Michael Douglas, and their relationship has been as tortured as many of those they've portrayed on the screen. The two, aided by family members and friends, give an evocative glimpse into their lives together and apart in "A Father . . . a Son . . . Once Upon a Time in Hollywood," a 95-minute documentary by Lee Grant that airs tonight at 8 on HBO.

There's something faintly queasy-making about the sight of these two actors as they sit before the camera, a Bundt cake and a bowl of lemons before them, and pretend to have a private conversation. But if you can get past that, you'll come out with a surprisingly faceted portrait of the two, Father Douglas in particular.

Through accumulated reminiscence -- the two principals speak separately as well as together -- Kirk Douglas emerges as a gigantic movie star, a man of some principle, a compulsively faithless husband and a harsh and neglectful father. His first wife, Diana -- Michael's mother -- speaks of him fondly but says she couldn't tolerate the "chronic infidelity." His second, Anne, who's been married to him for 51 years, recalls asking him at the outset to keep her apprised of his dalliances so that she would know they weren't important.

"But that pact was not kept," she announces without inflection: Kirk began carrying on in secret with a mutual acquaintance.

"I guess I was a bad boy," he says. "I have had lots of women in my life. Women to me are a byproduct of success."

And his was a great success story -- for many years he could have seemingly anything, or anyone, he wanted. But even now he speaks of a lingering hunger from his own childhood.

"Every son wants the approval of his father," he says. "And that was a tragedy of my life, because I never got it."

It's unclear whether Kirk Douglas realizes the extent to which this youthful deprivation was repeated on his own sons -- or whether he sees a connection. But Michael and his brother Joel make it clear.

"For a little kid he was intimidating," Michael says. "He could do anything. Anything."

And from Joel, whose weight problem annoyed his father: "When you had his full attention it could be devastating."

Though Kirk acknowledges all that, he's perhaps more interested in reminding Michael of the filial slights he's endured. The worst of these, we learn in a mildly testy exchange, involved "One Flew Over the Cuckoo's Nest" (1975). Kirk had bought the rights to the book years earlier, commissioned a dramatization, flopped in it on Broadway in 1963 and then embarked on a losing endeavor to transfer it to the screen. Enter Michael, who got that job done and claimed a Best Picture Oscar -- "in my movie, Michael, remember that" -- while Jack Nicholson won an Oscar in what had been Kirk's role.

"I coulda been a contender," Kirk jokes, but it's obvious that losing the part stung him badly. He asks Michael -- can it possibly be for the first time? -- how come he didn't get the job. Michael blames the director, says he tried to make it happen, and then answers in the language any movie star can understand: Nicholson was two decades younger, and Kirk's time had passed.

Hollywood observers have long speculated on the dynamic between father and son. To an outsider it seems clear that Michael felt the need to supplant, or perhaps become, his father. If that was the case, he did well at it: Kirk was a big star who became a successful producer; Michael was a third-tier actor who became a successful producer and from there moved on to stardom. Each fathered children with a first wife and then made a new family with a second wife. Kirk was the chronic philanderer. Michael seems to have been no slouch in that regard. (He does, however, denounce as a tabloid invention those reports that he was once treated for sex addiction.)

Grant intersperses her talking heads with numerous movie clips -- Kirk on the cross, Kirk getting aggressive with Barbara Stanwyck, Michael extolling greed, Michael trying to drown Glenn Close -- that lend velocity to her film while reminding us how significant these two men have been.

The other voices we hear, among them Jack Valenti, Kathleen Turner and producer Sherry Lansing, are mostly helpful. An exception is Catherine Zeta-Jones, Michael's second wife, who laughs coarsely and makes unconvincing fan squeals as she relates her nervousness at meeting Michael's father and suddenly realizing his father was Kirk Douglas. You'd think the silly cluck had never met a movie star.

Kirk Douglas's speech has been impaired since he suffered a stroke in 1996, and he can be difficult to understand. That frustrates him, understandably, but by the end of the film it's possible to see the affliction as, in Michael's words, "a blessing in disguise for him, because he's found peace."

In the years since his stroke, it seems, Kirk Douglas's competitive fires have subsided at last. He says he loves Anne more than ever, and she attests that the last few years have been their happiest.

If "Cuckoo's Nest" was the brilliant and public dividing line that marked the wresting away of the torch by the younger generation, that means Kirk and Michael Douglas have had three decades to come to terms with it. Like fathers and sons in countless other families, they both have and have not done so.

Toward the end, Kirk asks Michael, "Was I a good father?" The answer is perhaps not what he anticipated: "You have ultimately been a great father." It's an eloquent summation, as much for what it doesn't say as for what it does.

A Father . . . a Son . . . Once Upon a Time in Hollywood (1 hour 35 minutes) airs tonight at 8 on HBO.

"For a little kid he was intimidating," says Michael of Kirk.Michael and Kirk Douglas talk of their relationship in "A Father . . . a Son . . . Once Upon a Time in Hollywood."Jack Valenti, left, Michael Douglas, Catherine Zeta-Jones and Kirk and Anne Douglas, pictured last year, all have stories to tell in "Once Upon a Time."