In 2010, after the animation studio Illumination Entertainment's first film, "Despicable Me," became a surprise hit, its makers faced a quandary.

"Despicable Me" derived much of its appeal from the character of a curmudgeonly supervillain named Felonious Gru, voiced by Steve Carell, who begins the movie wanting to steal the moon and ends it by hanging up his shrink ray and adopting three orphans.

"Despicable Me" grossed more than $500 million worldwide, to the astonishment of Illumination founder and Chief Executive Chris Meledandri and the delight of distributor Universal Pictures, which promptly wanted a sequel. "What is a sequel going to look like, when you have this guy whose life has been about villainy, and you've taken him out of the role of active villain?" Meledandri wondered, when he and his directors, Pierre Coffin and Chris Renaud, started working on a follow-up.

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That question of how much a sequel can stray from the original without losing its essence was a constant concern in the making of "Despicable Me 2," which opened Wednesday. And it's a common quandary around Hollywood, which has 11 other sequels out this summer, from "The Smurfs 2" to "Iron Man 3" to "Fast & Furious 6."

There's a special craft to the sequel, and all sequels are not created equal. The best — "The Godfather: Part II," "Terminator 2: Judgment Day" — build on the strengths of the previous films. The worst — "The Godfather: Part III," "Terminator 3: Rise of the Machines" — forget what audiences liked about those movies in the first place.

For many artistic people in Hollywood, the idea of making a sequel is unappealing; it can feel at best uninspired and at worst craven. Yet sequels are a cultural staple going back to the ancient Greeks — "The Odyssey," after all, is really "The Iliad 2: Journey After the Sacking." Some sequels this summer manage to improve on the prior films in both critical reviews and box office — "Fast & Furious 6," for instance, has a 76% Rotten Tomatoes rating and $682.7 million at the global box office, while the original 2001 film earned a 63% fresh rating and $207.3 million.

But with sequels ever more popular among studios looking for a sure bet, many get greenlighted before they have a script or any clear creative raison d'etre — the recent "The Hangover: Part III," which saw its party boy protagonists return to the Las Vegas setting of the first film, had a CNN critic musing, "If only what happened in Vegas had stayed in Vegas." After the opening weekend, theater audiences largely stayed away too.

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"It's more often that somebody fails at a sequel than they succeed," said Andrew Stanton, who is directing his first sequel, "Finding Dory," a follow-up to his 2003 film, "Finding Nemo," for Pixar. "You don't want it to be derivative or redundant."

At Pixar, which released the prequel "Monsters University" this summer, sequels have been a source of debate. Although Pixar's parent company, Disney, is voracious for them, many at the animation studio, such as Stanton, have mixed feelings about making them.

"Finding Nemo," the studio's highest-grossing original film, seemed eminently franchise-able from a business standpoint.

"There was polite inquiry from Disney [about a 'Finding Nemo' sequel]," said Stanton, also a vice president at Pixar. "I was always 'No sequels, no sequels.' But I had to get on board from a VP standpoint. [Sequels] are part of the necessity of our staying afloat, but we don't want to have to go there for those reasons. We want to go there creatively, so we said [to Disney], 'Can you give us the timeline about when we release them? Because we'd like to release something we actually want to make, and we might not come up with it the year you want it.'"

In the case of "Finding Dory," the sequel will come after a long wait — 12 years — and explore the family background of Dory, a forgetful blue fish voiced by Ellen DeGeneres who was a sidekick in "Finding Nemo."

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Part of the art and craft of making sequels is knowing how to hold onto the original's audience while inviting in new people.

In the case of the "Fast & Furious" franchise, which has grossed $2.3 billion worldwide and has a seventh film due next July, that has meant pleasing its base — street racing fans — while drawing in women, Latinos and families.

"Some audiences may have dismissed the earlier films as being underground movies for people who love cars," said Adam Fogelson, chairman of Universal, the studio behind "Fast" and "Despicable Me" as well as the "Bourne," "Mummy" and "American Pie" franchises. "You want to broaden the audience from people who may have known about the first movie but may not have known it was a movie for them."

With the "Fast" movies, Universal has increased the budgets to allow for more crowd-pleasing set pieces, but the franchise's directors have kept cars a central part of the action. In "Fast 6," former street racer Dom (Vin Diesel), now working for the U.S. government, drives his car through the nose cone of a plane. The most recent installment went out on a limb and revived a favorite character among the series' female and Latino fans, Letty (Michelle Rodriguez), who had been killed off in a previous film.

"Street racing, while it still is carefully acknowledged, has moved into the background," Fogelson said.