Dean Karnazes (born Constantinos Karnazes) is a renowned American ultramarathon runner and author of the bestselling book Ultramarathon Man: Confessions of an All-Night Runner, which provides insights into ultra-endurance running for the general public.

Named by TIME magazine as one of the "100 Most Influential People in the World," Karnazes has pushed his body and mind to inconceivable limits. Among his many accomplishments, he has run 50 marathons in all 50 US states in 50 consecutive days. He’s run across Death Valley in the middle of summer and completed a marathon at the South Pole.

On ten separate occasions, he’s run a 200-mile relay race solo, competing alongside teams of twelve. His competitive achievements include winning the World’s Toughest Footrace, the Badwater Ultramarathon, and the 4 Deserts Challenge, racing in some of the hottest, driest, windiest, and coldest places on earth.

A New York Times bestselling author, Dean is a frequent speaker and panelist at many running and sporting events worldwide. An ESPN ESPY winner and three-time recipient of Competitor magazine's Endurance Athlete of the Year award, he has served as a US Athlete Ambassador in overseas sports diplomacy envoys to Central Asia and South America. He has twice carried the Olympic Torch and is a recipient of the President’s Council on Sports, Fitness, and Nutrition Lifetime Achievement Award.

Dean has raced and competed on all seven continents, twice. His incredible adventures have been featured on The Today Show, 60 Minutes, The Late Show with David Letterman, CNN, NPR, The Howard Stern Show, Late Night with Conan O’Brien, Jimmy Kimmel Live!, the BBC, and many others. He has appeared on the cover of Runner’s World, Outside, and Wired magazines, and has been featured in TIME, Newsweek, People, GQ, The New York Times, USA TODAY, The Washington Post, Men’s Journal, Forbes, The Chicago Tribune, The Los Angeles Times, and the London Telegraph, to mention a few.