As Pixar Animation returns to its most successful franchise, “Toy Story,” for a fourth movie, John Lasseter, the studio’s chief creative officer says “Toy Story 4” will be a love story that picks up where the previous film left off, with Woody, Buzz Lightyear and the rest of the series’ toy chest of characters handed down to a little girl named Bonnie.

Lasseter says that, though a lot of industry people think Pixar does sequels only for the company’s bottom line, “for us it’s pure passion — we only make sequels when we have a story that’s as good as, or better than, the original.”

That philosophy sets a high bar for the forthcoming film. The first three have grossed more than $1.3 billion worldwide and garnered mostly positive reviews for their storytelling and technique. Installment 3, directed by Lee Unkrich in 2010, won Oscars in the animated feature and original song categories, and became only the third animated movie in history to get a best picture nomination.

While “Toy Story” and its merchandising and theme park extensions are important financially to Disney, which owns Pixar, the series’ characters are crucial parts of Pixar’s — and Lasseter’s — creative identity. He directed the original 1995 film — Pixar’s first feature film, which revolutionized animation. Today that industry is almost exclusively computer driven.

In addition to the three “Toy Story” feature films, its characters also have appeared in three short films and two TV specials, including “Toy Story That Time Forgot,” which premiered on ABC on Dec. 2.

The idea for a fourth film germinated, says Lasseter in a phone interview, during a lunch in his Emeryville office with Pixar executives Pete Docter, Andrew Stanton and Unkrich.

Over the past two years Lasseter and Stanton wrote a story treatment and pulled in other writers, including Rashida Jones and Will McCormack after seeing their 2012 comedy, “Celeste and Jesse Forever,” about a divorcing couple who try to remain friends.

“They have such a great sense of character and originality,” Lasseter says of Jones and McCormack, “and I wanted to get a strong female voice in the writing of this.”

The last film directed by Lasseter, 2011’s “Cars 2,” performed well at the box office internationally but was a rare critical misfire for the studio.

Lasseter says he will work on “Toy Story 4” while continuing his Disney duties, which include heading Walt Disney Animation and Disneytoons and serving as the principal creative adviser for the company’s theme park designers.

“One of the things that was very important for me, as an artist, is to continue directing,” Lasseter says. “When I direct, I get to work with the individual artists, with the animators. It’s very important to keep young talent coming into the studios … to get back in and help tell stories.” He says he will continue to commute weekly to the Disney lot in Burbank.

Asked whether it might be difficult for his staffers to tell the boss if they think his movie isn’t working, Lasseter says he and Disney-Pixar President Ed Catmull have attempted to create an environment that fosters candor. “We work really hard to create an atmosphere where people feel like they can be honest, without retribution,” he says.