If you've swum in an open water event, you've probably noticed Dr. Paul Kiell. At 74-years of age, the tireless Kiell — who has participated in five relay swims around Manhattan (2001-2005) and numerous individual events such as the Governors Island Swim, the Chesapeake Bay 4.4-Miler and the Alcatraz swim — tends to stand out even on the rare occasions when he isn't the oldest swimmer present.

A competitive swimmer in high school and at Washington and Jefferson College — where he was named co-captain during his senior year — Paul abandoned swimming and joined the jogging boom of the late 1960s. Over the next 30-odd years he ran more than 50 marathons — including Boston 17 times — and several ultramarathons.

Paul "reluctantly" returned to swimming a few years ago when a serious leg injury forced him off the roads. He became involved in open water swimming because "it's the closest thing to road races. You can get lost in the crowd, look at nice scenery and enjoy the camaraderie of a shared ordeal with some extraordinary people."

To Paul's disappointment, few of those extraordinary people are in his age group. "I wonder why more people my age haven't gotten involved. We're doing something that is natural and basic — we're playing." Should any of his contemporaries seek to take up his challenge, he offers this advice: "Stay active in everything you do and stay young, which at my age is accomplished by avoiding looking in the mirror and not taking too many pictures."

Like any good doctor, he follows his own prescription. In addition to the psychiatry practice he's maintained for more than four decades, Paul is the author of two books: Keep Your Heart Running: A Graduated Total Health and Fitness Program for People of All Ages (written with Joseph Frelinghuysen) and Exercise and Great Minds, which examines the exercise practices of some of the great thinkers of the 20th Century. A third book, on the life of Glenn Cunningham, a world-record runner in the 1930s, is set for publication next year.

In his spare time, Paul enjoys gardening, reading historical novels, listening to Louis Armstrong's recordings from the 20s and 30s, and spending time with his family. He and Benita, his wife of 49 years, have four daughters and one son — all of whom have run at least one marathon with their father — and six grandchildren.

How can you best sum up a man like Paul? Oddly enough, the best answer comes from a man who doesn't even know him, a fisherman who, during the 2004 Manhattan Island Marathon Swim, spotted Paul swimming steadily up the East River and yelled out, "He's my hero!"