“You’re on in 45 minutes, Mark.”

Talk about a rush. Understudy Mark David Kaplan had less than an hour to ready himself to perform in front of thousands of people in a nationally touring production of “The Lion King.”

Unfortunately, the makeup for his character, Zazu the majordomo (the king’s chief servant) requires more than an hour to apply.

“I had two people — four hands — on me. I just shut my eyes and let them do the work,” said Kaplan, who can now laugh about the incident (the show did go on).

The play, based on the eponymous animated Disney movie, is currently playing at San Francisco’s Orpheum Theatre until September, when, “In true Disney fashion, I’m sure they’ll extend,” said Kaplan, a 41-year-old, well-traveled Jewish actor.

So far (“Knock on wood!”) Kaplan hasn’t had to assume one of the three parts he understudies mid-show. But, playing the bird Zazu or Pumbaa and Timon, Kaplan finds his way onto the stage roughly every fourth show, which is twice a week.

If readers think it’s odd that an understudy would find himself in the midst of the show one day out of four, then they probably haven’t seen “The Lion King,” quipped Kaplan.

This isn’t just a show. It’s an event. And the actors work harder than Clydesdales while buried under bulky costumes. Many actors also operate elaborate puppets that run, fly, gesticulate and even roll their eyes.

Backing up three parts “is one of the most varied things I’ve ever done. Cardiovascular and endurance-wise, it’s one of the most challenging. In particular, Zazu moves around a lot. There’s a lot of forward rolling, running into walls, chasing young lions and also expressing it all through the puppet; making him fly, moving his wings and making his eyes and mouth move. It’s pretty darn crazy,” he says. “Once you see the show, you can understand how [an actor] might want a day off.”

Even if Kaplan makes it out onto the stage, you’d be hard-pressed to recognize him under layers of makeup and quasi-mechanical costumes.

The Timon outfit features a harness attached to Kaplan’s sternum, to which a full-body sized rodent puppet is attached. For the warthog Pumbaa, Kaplan is swaddled in clunky jodhpurs, a warthog head and a huge, black mohawk wig. Depending upon which character he plays, his face will be painted purple, green or blue and white.

Portraying a singing warthog on stage is a long way from Kaplan’s beginnings in theater, when he and other Jewish friends strummed the guitar and sang at Hadassah events.

Kaplan’s parents were both musicians, and he notes that studying for your Haftarah is always easier when your mom and dad sing and play the trumpet and piano. Both of Kaplan’s siblings are also professional actors.

Not surprisingly, one of the biggest parts of Kaplan’s Jewish upbringing involved singing and playing music. Even as an adult, when he attends services while visiting his cousins in Brookline, Mass., he realizes that “no matter where you grew up in this country, we all sing the same songs. That gives me a little shiver.”

Kaplan broke into the Chicago theater scene nearly two decades ago, and made the all-important transition to New York afterwards. Throughout “The Lion King” he’ll be living in Oakland with his dog, Stomper.

While many casual theatergoers assume being an understudy is a demotion, Kaplan doesn’t see things that way. Covering three different parts requires great versatility, and Kaplan enjoys playing each character. “Every show is different,” he said. “Thank God, every show is different.”

For more information or tickets to “The Lion King,” call (415) 356-LION or visit http://disney.go.com/disneytheatrical/lionkingsf/.