The best actors get lost in a role. Al Pacino does just that in “You Don’t Know Jack” (8 p.m., Saturday, HBO). The Pacino you know from “The Godfather” movies, “Scent of a Woman” and a generation of memorable films vanishes as he becomes the celebrated, notorious, iconic and — to director Barry Levinson — a deeply misunderstood American original, Dr. Jack Kevorkian.

Pacino’s Kevorkian is both a visionary and a misfit, a regular Detroit guy with a Midwestern accent who spends his downtime playing Bach on a flute and scouring yard sales for medical equipment. His entourage — and that’s too strong a word — includes his best friend, Neal (John Goodman), and his offbeat sister, Margo, played by Brenda Vaccaro, an acting contemporary of Pacino’s, gloriously rediscovered for this role. Susan Sarandon appears, in the least-fashionable clothes and hairstyle imaginable, as Janet Good, a Hemlock Society activist. Danny Huston rounds out the cast as Geoffrey Fieger, a larger-than-life activist lawyer who moves to the center of Kervorkian’s life.

There’s no getting around the fact that this movie is about the man known as “Dr. Death,” an advocate of physician-assisted suicide who became the center of a national debate in the 1990s. And the film is filled with harrowing moments. But “You Don’t Know Jack” is best appreciated as a character study, an exploration of the unexpected, and, at times, unsettling private sides of a public figure. The title says a lot. But after Pacino is through with Jack, we know a whole lot more.

l Winona Ryder stars in “When Love is Not Enough” (8 p.m. Sunday, CBS), a Hallmark Hall of Fame Presentation. You know something is up when the narrator (Ryder) mentions the word “alcoholic” in the first minute of the voiceover. We soon learn that Ryder (“Age of Innocence,” “Dracula”), who seems to have been born to play period costume dramas, portrays Lois Wilson, the co-founder of Al-Anon and the wife of Bill Wilson, the founder of Alcoholics Anonymous.

Ryder performs admirably as an ardent figure. She gives voice to the spouse of the substance abuser, a person rendered invisible first by addiction and then overlooked during the difficult process of recovery. Barry Pepper, who was outstanding as Roger Maris in “61,” is impressive here as Bill Wilson, a man overmatched by Wall Street and alcohol, who puts his entrepreneurial and sales skills to work in an entirely different direction.

l As the title implies, the four-part series “Into the Universe With Stephen Hawking” (8 p.m. Sunday, Discovery) tackles the really big ideas. The author and physicist offers a glance at the Big Bang and the beginning of the universe, as well as theories about its eventual end. Along the way, he offers thoughts about the possibility of life on distant planets and what that might look like.

l Liev Schreiber narrates “America The Story of Us” (8 p.m. Sunday, History), a 12-part history of the United States that the History Channel has promised to make available to every school and college in the country. Like any history of a subject so vast, “Story” settles on a series of big events, major ideas and informative biographies to take the story from the settling of Jamestown in 1607 to more recent years.

The production puts particular emphasis on special effects and the role of the natural world in history’s unfolding. We see the ships that brought colonists to the New World from a fish’s perspective. As the British prepare to invade Manhattan during the Revolutionary War, we’re shown a modern-day New York before computer graphics strip the island of its buildings and restore it to a world of trees and streams with only 20,000 residents.

Long gone are the days when History Channel documentaries used rather cheap-looking re-enactments and stock silent movie footage. This is an impressive production with many cinematic elements. We’re told more than 130 historians were consulted. And along the way, we also hear from Sheryl Crow, Soledad O’ Brien, David Baldacci, Meryl Streep, Donald Trump and Michael Douglas, among others.

Saturday highlights

• Eddie Murphy plays numerous roles in the 2007 comedy “Norbit” (7 p.m., ABC).

• A young painter (Bryan Greenberg) falls for an older woman (Uma Thurman) a little too close to home in the 2005 romantic comedy “Prime” (7 p.m., TBS) directed by Ben Younger. Greenberg’s character here is not terribly different from his role on HBO’s “How to Make it in America.”

• Back to the future on “Doctor Who” (8 p.m., BBC America).

• Gabourey Sidibe (“Precious”) hosts “Saturday Night Live” (10:30 p.m., NBC), featuring musical guest MGMT.

Sunday highlights

• The new series “The Real Story” (7 p.m., Smithsonian) looks at elements of fact behind best-selling thrillers and movies. Tonight: some of the real events that helped inspire “The Exorcist.”

• “Small Island” concludes on “Masterpiece” (8 p.m., PBS, check local listings).

• The eighth annual TV Land Awards (8 p.m., TV Land) glances back. This year, “The Love Boat” receives the fan favorite award.

• Japanese forces on Peleliu refuse to surrender on “The Pacific” (8 p.m., HBO).

• Elder-care issues take center stage on “Brothers & Sisters” (9 p.m., ABC). Marion Ross guest stars.

• Just when you thought it was safe to go back in the fresh water, “River Monsters” (9 p.m., Animal Planet) enters its second season.

l The Iowa State Fair becomes a crime scene on “On the Case with Paula Zahn” (9 p.m., Investigation Discovery).