On the planet of "coulda-shoulda-woulda," you'd find Will Smith playing Prot, the quirky fellow who claims to be an alien in K-PAX (opening today). Instead, two-time Oscar winner Kevin Spacey aptly fills the character's gravity boots. Indeed, during its seven years in the making, K-PAX wended its way through quite a diverse casting process — to say the least! — that altered the film completely.

Screenwriter Charles Leavitt actually envisioned actor John Cusack as the lead alien while adapting Gene Brewer's novel for film. But it was Men in Black spacebuster Smith who originally became attached to star. Nearly two years later, the movie stalled due to "creative differences," and producers went in search of a new Prot.

"We had lists and lists of possibilities," producer Lawrence Gordon (Field of Dreams) tells TV Guide Online. "We discussed Prot being a young, young actor or an old, old actor. We could've made this a number of different ways, but the minute we heard that Kevin was interested at all... he's the perfect Prot. He's just the perfect guy. He's got the dimension. He's got the power and the humor. He's the whole package. And I think it's a great performance."

Casting Prot's psychiatrist proved another tricky fork in the road. Though the part was written for a man, producers toyed with casting Meryl Streep as Spacey's shrink. "It would have brought in another layer, which would have been a sexual dimension," admits producer Lloyd Levin (Boogie Nights). "That might have been distracting from this particular story." And it might've made the film too similar in style to 1984's Starman, which garnered Jeff Bridges an Oscar nod for playing a misunderstood alien.

In a wacky twist, Bridges himself was cast as the K-PAX head doctor, giving the flick a one-two punch that's already led to Oscar buzz. "Watching them work every day was like watching an acting event," enthuses Gordon. "I've never seen anything like it. This was the most enjoyable of all the films I've been involved in."