When it comes to assisted suicide, it is possible to love the sin and hate the sinner. That’s how many feel about Jack Kevorkian — plenty of those who favor mercy killing draw the line at Dr. Death

“You Don’t Know Jack: The Life and Deaths of Jack Kevorkian,” a film onHBO on Saturday, tells the story of Dr. Kevorkian, the Michigan pathologist who has, for better and for worse, cemented his name to one of the more disturbing ethical issues of our time. And by casting Al Pacino as Dr. Kevorkian, the creators have given themselves an extra degree of difficulty.

A biographical film almost inevitably tilts in sympathy with its subject; that’s why so many people object to any effort to cinematize Hitler’s life story or Stalin’s. A credible biography of Dr. Kevorkian has to focus on the self-serving zealotry beneath the martyr’s guise, but Mr. Pacino has a subversive gift for tapping into the endearing underside of the most despicable villains.

So it is a credit to Mr. Pacino that while he burrows deep into the role, he never lets Dr. Kevorkian’s crackpot charm overtake the character’s egomaniacal drive. Susan Sarandon, plain and bespectacled, is just as agile as Janet Good, a local Hemlock Society leader who made common cause with Dr. Kevorkian — despite his lack of social graces. And it is a credit to the filmmakers that a movie dedicated to a fearless, stubborn man’s campaign against the medical establishment and the criminal justice system doesn’t overly romanticize his struggle or exonerate him from blame.

No film about euthanasia, no matter how sensitively written, can avoid offending one side or the other; at best, both sides will find reason to complain. More important, “You Don’t Know Jack” is a compelling, at times thrilling, tale that can absorb even those with little interest or feeling for the subject. This is one of the saddest, dreariest subjects imaginable, but “You Don’t Know Jack” is anything but.

The two sides of the man nicknamed Dr. Death — his passion for the right to die and his blinkered egotism — are presented up front. The movie begins with Dr. Kevorkian peering through a glass window into a hospital room, where an old woman tethered to life-support tubes looks despairingly at him.

“You know, she had that same look of agony on her face, just like Mother,” he says to his sister Margo (Brenda Vaccaro). “It’s not living, you know, it’s not being alive.”

Moments later this retired pathologist is shown poring through books about euthanasia in Europe, and planting his flag on the map of scientific progress. “I don’t know why I didn’t think of this sooner, I was limiting myself,” he mutters.

Margo urges him on: “It will be your own field of specialty, Jack. You’re going to need business cards, you know.”

The doctor’s desire to be recognized is one of the seeds of his undoing, and the film doesn’t leave his outsize ambition unexplored. Packing the back of his Volkswagen van with the bottles, tubes and metal rods that make up what he calls “the mercitron,” to administer his first assisted suicide, Dr. Kevorkian is buoyant.

“This is what you do it for, to be able to put your stamp on medical history,” he tells his friend and helper, Neal Nicol (John Goodman).

Mr. Pacino is almost unrecognizable in a shock of puffy white hair and oversize glasses: he looks like an elderly John Turturro. Speaking in a flat Michigan accent, the actor manages to convey Dr. Kevorkian’s placid tone and occasional flecks of dry humor without masking his reckless indifference to public sentiment and professional caution. His anger is chilling, as when he hangs up on Janet Good after she has second thoughts about letting him use her house for his first assisted suicide.

“There’s nothing further to be gained by talking to you,” he says, banging down the phone.

“He had virtually no authentic human warmth” is how Jack Lessenberry, one of the first reporters to interview Dr. Kevorkian and who is portrayed in the film by James Urbaniak, described him in an article.

The film, directed by Barry Levinson, looks at times like a documentary, inserting Mr. Pacino into real archival footage, including the infamous 1998 Mike Wallace segment on “60 Minutes” that showed Dr. Kevorkian administering a lethal injection to Thomas Youkand daring the authorities to stop him.

They did. (He was convicted of a single charge of second-degree murder in 1999, sentenced to a 10-to-25-year prison term, and was released on parole for good behavior in 2007.)

Dr. Kevorkian taped his patients, creating a video record of their concerns and consent, and a few of those poignant, real-life interviews are also worked into the film. Others are skillful re-creations, including scenes with his first patient, Janet Adkins, who at 54 was only beginning to show symptoms of Alzheimer’s disease when she asked Dr. Kevorkian to help her die.

“She looks well to me,” Kevorkian says to his sister after watching a film of Mrs. Adkins. “She looks quite capable.”

Margo, relieved, agrees, adding, “She’s not the right one.”

Her brother bristles.

“But she has the right,” he retorts. “As a patient, it’s her choice.” He begins shouting: “What do we care about the media? Who cares?”

Dr. Kevorkian, who cared deeply about explaining himself to the news media, never seemed to understand, or care, how much his doctrinaire rhetoric — comparing American treatment of the terminally ill to Nazi experiments or describing the United States as totalitarian — hurt his own cause. Nor did it help that he was so heedless of medical propriety, second opinions or legal constraints, relying on a patient’s word and his own judgment over anything else.

The film captures his zeal, his self-righteousness and also the creepy tawdriness of his right-to-die practice: the macabre, ghastly art works he painted himself, sometimes with his own blood; his shabby apartment; his rickety DIY death contraptions; and the battered van he used as a death chamber. Even Margo is shocked by how makeshift and crude the process is, exclaiming after the first assisted suicide in his van, “I guess somehow I just thought the whole thing would be nicer.”

Unpopular causes rarely find the most persuasive champions, and sometimes only the least eloquent are willing to speak out. “You Don’t Know Jack” takes a considered and insightful look at the frail, elderly man whose embrace of death gave him a reason to live.

You Don’t Know Jack

The Life and Deaths of Jack Kevorkian

HBO, Saturday night at 9, Eastern and Pacific times; 8, Central time. Directed by Barry Levinson; written by Adam Mazer; Steve Lee Jones, Lydia Dean Pilcher, Glenn Rigberg, Tom Fontana and Mr. Levinson, executive producers; Scott Ferguson, producer. Produced by Bee Holder Productions, Cine Mosaic and the Levinson/Fontana Company. WITH: Al Pacino (Dr. Jack Kevorkian), Susan Sarandon (Janet Good), Danny Huston (Geoffrey Fieger), Brenda Vaccaro (Margo Janus) and John Goodman (Neal Nicol).