Robin Williams, star of Disney's 1992 hit Aladdin, is the reason most animated movies now star celebrities rather than professional voice actors:

The marketability of a big-name celebrity voice actor gave way, perhaps inevitably, to an even more insidious trend: directly basing a character's appearance on the famous actor providing its voice. The examples range from the Jerry Seinfeld bee in Bee Movie to the Tina Fey-esque reporter in Megamind, but the apex is Dreamworks' 2004 animated film Shark Tale, which features creepy human-fish hybrids of actors like Will Smith and Angelina Jolie.

Pixar, ahead of the curve as always, has attempted to back away from relying on A-List actors, with terrific results; the studio's two best films in recent years (and, arguably, of all time) are Wall-E­—whose robotic leads can only speak variations of their names—and Up, which starred Ed Asner and newcomer Jordan Nagai.