Sheck Exley was a teacher of advanced algebra and calculus at Suwanee High School in Live Oak, Florida. The man is better-known, however, for his pioneering work as a cave diver. He broke numerous world records in the sport, and was also a successful author on the subject. He published Basic Cave Diving: A Blueprint for Survival (1986) and Caverns Measureless to Man (2009), whose title was inspired by a phrase from the poem “Kubla Khan” by Samuel Taylor Coleridge.

This naturally-talented educator spent years training advanced divers, and those experiences fueled his passion for teaching. A popular teacher, he even posted his home number on the bulletin board and told his students they could call him day or night if they had trouble with their math homework. Before long, the kids were calling him with troubles that had nothing to do with differential equations. Over time Sheck became a mentor to adolescent boys who had brushes with the law or were on the verge of dropping out of school. One by one, he pulled them into the local karate club he founded, teaching them how to avoid trouble through physical and mental discipline, to take control of their lives, and to make better decisions.

Sadly, Sheck’s own life story does not have a happy ending. He died while attempting to set a new world depth record in a cenote, or sinkhole, known as El Zacaton in Tamaulipas, Mexico, on April 6, 1994. He was only 45.