Harmon was born in Portland, Oregon on Oct. 18, 1942. He graduated from Clackamas High School and attended Portland State University where he earned an accounting degree.
He lived in Seattle for a short time, working for Boeing, then returned to Portland to work for Freightliner. He later established his own certified public accountant practice in Olympia. In 1989, he went into the business of manufacturing and selling greenhouses. He married Sherry Correla on March 30, 1991, in Vancouver, Wash. He moved to McMinnville in 1991 and Amity in 1996.
In addition to chess Harmon also enjoyed horses, horse camping at the beach and reading. He was known for his an easygoing, mild-manners and for being very non-judgmental and a man who took everyone at face value.
Harmon was heavily involved in chess organization in the Northwest (the states of Washington and Oregon). In 1965, while living in Renton, Washington he served as President of the Washington Chess Federation.
By 1967 he had returned to Portland and helped organize the Oregon Chess Federation and served as its first president. That same year Harmon worked with the Oregon Museum of Science and Industry to start a series of Oregon scholastic chess tournaments.
Harmon was a skilled blindfold chess player who as a teenager Clark once played a series of 5-minute games with the board out of sight against other players close to his ability. In the late 1970's he had been invited to conduct a blindfold simultaneous exhibition at a Portland area mall. He wasn't sure whether to accept, so he wanted to practice. He had the Portland State University Chess Club invite six players whose average rating was about 1800-1900 to a private blindfold simul. During that exhibition there were two side-by-side games in which his opponents were playing nearly the same opening but the games were different enough to try to confuse him. On a couple of occasions he struggled, but in the end he prevailed after 3 or 4 hours and a lot of cigarettes, with three wins, a draw, and two losses. Finding the effort exhausting, he decided not to accept the invitation.
Harmon also briefly tried his hand in two postal chess tournaments: the US Absolute, with moderate success when he finished tied for 4-6 place (out of 13) scoring +6 -4 =2. He earned $13.33 for his efforts. Earlier he had placed second in the U.S. CC Championship.
In the following game he defeats the legendary Walter Browne using the discredited Budapest Gambit! Despite an early debut in 1896, the Budapest Gambit received attention from leading players only after a win as black by Milan Vidmar in 1918. It enjoyed a rise in popularity in the early 1920s, but nowadays is rarely played at the top level. It experiences a lower percentage of draws than other main lines, but also a lower percentage of wins for Black.