Ashton Kutcher is world's "happiliest" married man

LOS ANGELES (Reuters) - The planet's "happiliest" married man, Ashton Kutcher, was once a champion carouser until he met his wife five years ago and became a changed man.

So when Kutcher set out to make his new movie "What Happens in Vegas," which opened on Friday, he drew on his rowdy bachelor days -- as well as his three-year marriage to actress Demi Moore -- to play the role of a chronic underachiever who accidentally marries the girl of his dreams.

"I never really thought I would get married," Kutcher told reporters ahead of the film's release. "I watched my parents go through a divorce and I thought, 'This is not something anybody should do.' Why put a legal document on top of a really great relationship?"

His character, Jack Fuller, may be an underachiever. But the same cannot be said of the 30-year-old Kutcher.

He rose to fame playing a high school stoner on television comedy "That '70s Show," then parlayed his TV success into a career in films such as "The Butterfly Effect" and "Bobby."

The former biochemical engineering student at University of Iowa also has produced reality television programs such as prankster show "Punk'd."

When he began dating Moore back in 2003, few Hollywood watchers believed the relationship would last because she is some 15 years his senior. But the pair were married in 2005, and by all accounts are happy.

"I knew she was the person I wanted to spend the rest of my life with," he said. "I am the happiliest -- I think I just invented that word -- married guy on the planet."

JACK & JOY

If only the same could be said for Fuller, who manages to lose his job at his father's closet factory at the same time as Joy McNally, played by Cameron Diaz, is dumped by her fiance at a surprise birthday party she threw for him.

Each flies to Vegas on a whim and, with their best friends in tow, create a new set of problems when they wake up married, then win a $3 million slot machine jackpot together.

The mismatched pair spend most of the film trying to trick each other out of the money as they serve a sentence of "six months hard marriage" handed down by Judge Whopper (Dennis Miller), who wants to punish them for their impulsive vows.

Kutcher said the circumstances of his own top-secret wedding to Moore were far removed from the boozy, spur-of-the-moment nuptials depicted in "Vegas."

He and Moore lured about 45 friends and family members to their home for the wedding by inviting them to a "housewarming," Kutcher said.

When his mother, who was not in on the secret, arrived to find Moore trying on her wedding gown and veil, she turned to Kutcher and said, "We don't wear dresses like that to housewarmings where I come from," he said, laughing.

Kutcher said he has drawn lessons about marriage from Rabbi Yehuda Berg at the Kabbalah Centre in Los Angeles where he and Moore and other celebrities study.

While men regard sex as the apex of a relationship and women focus on the wedding, "everybody is missing what happens after that," he said.

"It's like if you ... got hired at a new job and you showed up and didn't work, you'd probably get fired pretty quickly," Kutcher said. "Once they get married, (people) think, 'All right, the work is done,' when really you just got the job."

(Reporting by Gina Keating; Editing by Bob Tourtellotte and Xavier Briand)