Tough Mudder is an endurance event series in which participants attempt 10–12 mile-long (16–19 km) military-style obstacle courses. It was designed and created by Will Dean (businessman), a British Harvard Business School post graduate and a former corporate lawyer, and tests mental as well as physical strength. The obstacles often play on common human fears, such as fire, water, electricity and heights. The main principle of the Tough Mudder revolves around teamwork. The Tough Mudder organization values camaraderie throughout the course, designing obstacles that encourage group participation. Participants must commit to helping others complete the course, putting teammates before themselves, and overcoming fears. An average 78% of entrants successfully complete the course. The first Tough Mudder challenge was held in the United States in 2010. To date, more than 2.5 million people worldwide have participated in Tough Mudder events, making it one of the world’s fastest-growing athletic activities, that draws between 10,000 and 15,000 participants per event. Tough Mudder currently employs over 150 people worldwide. Tough Mudder was co-founded in 2010 by Will Dean and Guy Livingstone, both British citizens living in New York. Dean had developed the idea for the company while studying at Harvard Business School, where the concept was a semifinalist in the school’s annual business plan competition. It has been noted that Will Dean took the idea from Billy Wilson and his Tough Guy races. Dean and Livingstone held the first Tough Mudder event on May 2, 2010 at Bear Creek Ski Resort near Allentown, PA. Promoted exclusively through Facebook advertising and word of mouth, the event drew more than 4,500 participants.