Here are 20 celebrities who worked hard to finish marathons, whether to raise money for a cause, lose weight, or rebound from a setback.

One of the hardest parts about getting healthy and strong is believing that we can change our lifestyle and achieve our goals. Training for a marathon might seem like an overwhelming, if not impossible, journey towards wellness, but it can give you a concrete goal to work on every day, gradually transforming your body and your perspective on health and fitness. Here are 20 celebrities who worked hard to finish marathons, whether to raise money for a cause, lose weight, or rebound from a setback.

Princess Beatrice: Twenty-one-year-old Princess Beatrice was the first royal to complete a marathon, finishing the London Marathon tied to over 30 friends in April 2010.

Sean Combs: Then known as P.Diddy, Sean Combs finished the New York City Marathon in 2003, despite suffering seizing legs at mile 12. He finished in 4:14:54.

Mario Lopez: Knockout Fitness writer — and oh, yeah, A.C. Slater — actually was a wrestler in real life as a kid but got into running when he was older. He ran the Boston Marathon in 2002 for the Big Brothers Big Sisters of America charity.

Richard Branson: Entrepreneur Richard Branson also ran with Princess Beatrice in the 2010 London Marathon. The 60-year-old ran to raise money for Virgin Unite.

Dexter Holland: The Offspring rocker ran the Los Angeles Marathon in 2006 to support the Innocence Project, which helps facilitate post-conviction DNA testing.

Anthony Edwards: The former ER doc has run two marathons: The Chicago Marathon in 2003 — he finished in just under four hours — and also the New York City Marathon in 2009 to help fund a pediatric clinic in Kenya.

George W. Bush: Former President George W. Bush was one of the fittest presidents in American history, and resolved to train for a marathon just a month before the race. He finished the 1993 Houston Marathon in 3:44:52.

Billy Baldwin: Those Baldwins are known more for their husky voices and cockroach-worthy abilities to stay at the forefront of American pop culture than their athleticism, but Billy Baldwin finished the New York City Marathon in 1992, in under 3 1/2 hours.

Al Gore: Al Gore was more mountain man than politician after losing the 2000 presidential race, but the former VP and environmental activist completed the 1997 Marine Corps Marathon in 4:58:25.

Will Ferrell: This next celebrity really threw us. We'll always remember Ferrell's Old School streaking moment, but apparently he ran the Boston Marathon in 2003 with his wife.

Mike Huckabee: Another former presidential candidate and marathon runner is Mike Huckabee, who lost over 110 pounds during the time he served as governor of Arkansas. He has also finished four marathons, including the Marine Corps Marathon, the Little Rock Marathon (twice) and the New York City Marathon.

Oprah Winfrey: Oprah has had her share of weight gain and loss stories, but in 1994 she took on a new challenge: to inspire people who never thought they could run a marathon to finish the race. Oprah finished the Marine Corps Marathon in 4:29:20, mostly under the radar, as media hype focused on the talk show host running in Chicago later that year.

Meredith Baxter: The same year that Meredith Baxter began acting on Family Ties, she completed the New York City Marathon, finishing at just over 4 hours.

Katie Holmes: Actress Katie Holmes has said that she got into running after giving birth to daughter Suri, and she ran the New York City Marathon in 2007. Conspiracy theorists love speculating over Tom and Katie's less traditional lifestyle (Scientology baby monitors, anyone?) and her marathon time is no exception.

Charlie Gibson: Former GMA and World News anchor Charlie Gibson was a friendly face on network TV, but he loved showing off his ferocious interview and moderator skills, catching politicians in twisted stories and confusing declarations. Back when he was younger, and maybe a little more docile, Gibson ran the 1983 Marine Corpos Marathon, finishing under 4 hours.

Shia LaBeouf: LaBeouf's career can go two ways right now: he can either become a big blockbuster action star or temper towards his fairly successful track in more serious dramas. But the young actor is also trying to clean up his image — and maybe his lifestyle — he ran the Los Angeles Marathon in March, 2010.

Dana Carvey: Back in 1972, Dana Carvey clocked what could be the fastest celeb marathon time: 3:04:21 at the Ocean to Bay Marathon.

Ted Koppel: TV journalist Ted Koppel also ran the 1983 Marine Corps Marathon, finishing well behind Charlie Gibson.

Alanis Morissette: Singer and actress Alanis Morissette ran with Ed Norton and David Blaine to support the Maasai Wilderness Conservation Trust at the New York City Marathon in 2009.

Sarah Palin: Back when Sarah Palin was just a simple hockey mom, she finished the 2005 Humpy's Marathon in Alaska in 3:59:36.