Action stars with a sense of the silly tend to have longer careers. Proof of this theory can be found all over the Saturday dial. Few of life’s quirks mystify me more than the career of Vin Diesel. But he is savvy enough to appear in light fare like “The Pacifier” (7 p.m., today, ABC), where he plays a Navy SEAL assigned to baby-sit, or rather bodyguard, the family of a government big shot. Arnold Schwarzenegger (“Kindergarten Cop”), who practically pioneered this school of muscle-bound comedy, appears in “Terminator 3: Rise of the Machines” (7 p.m., today, AMC), “Terminator 2: Judgement Day” (9:30 p.m., today, AMC) and the cloning drama “The 6th Day” (9 p.m., today, FX).

Contrast the sustained success of Schwarzenegger and Diesel with the fates of Steven Seagal and Jean-Claude Van Damme. Spike has programmed an all-day Seagal vs. Van Damme marathon today from noon today to 2 a.m. Sunday. Fans of such fare as “In Hell” (6 p.m.) and “Belly of the Beast” (8 p.m.) should rejoice. Of course, the stars of “Wake of Death” (2 p.m.) and “Out for a Kill” (4 p.m.) aren’t the only martial artists to turn their names and careers into a punchline. When is the last time we saw Chuck Norris except at Mike Huckabee rallies?

• I’ve long felt that some of the more memorable sitcoms are perverse twists on tragedy. In many ways, “The Beverly Hillbillies” was “The Grapes of Wrath” with a laugh-track. In a remarkably similar vein, the new comedy “The United States of Tara” (9 p.m., Sunday, Showtime) tries to find the funny in such wrenching dramas like “Sybil” and “The Seven Faces of Eve.”

I’m no mental health expert, so I will leave the legitimacy of the multiple personality disorder to others. But it certainly provides a memorable acting showcase. In “Tara,” Toni Collette gets to play mother and housewife Tara as well as three alternate personalities that tend to show up during times of stress. There’s T, a thong-wearing and baring teenage shopaholic; Buck, a hard-drinking male veteran and Alice, a perfect 1950s housewife. Like an acting workshop, or improvisational exercise, Tara’s family also reacts rather seamlessly to Tara’s transformations. Husband Max (John Corbett), daughter Kate (Brie Larson) and son Marshall (Keir Gilchrist) appear to welcome and indulge these “visitors,” safe in the knowledge that Tara will return.

It’s interesting to note that “Tara” was created by Diablo Cody, who wrote the 2007 comedy “Juno.” Both “Tara” and “Juno” feature young characters who are wise beyond their years and show off a startling knowledge of pop culture of decades past. Juno was a punk aficionado. Tara’s son Marshall offers university-level lectures on the silent films of Louise Brooks and plays Thelonious Monk to drown out T’s tantrums.

“Tara” would be disturbing if it weren’t so obviously contrived and so smugly sure of its own outrageousness.

Today’s highlights

• Rosario Dawson hosts “Saturday Night Live” (10:30 p.m., NBC), featuring musical guest Fleet Foxes.

Sunday’s highlights

• Musicians celebrate a new administration in “We Are One: The Obama Inaugural Celebration at the Lincoln Memorial” (7 p.m., HBO).

• “Flight of the Conchords” (9 p.m., HBO) enters its second season.