Faced with the prospect of his upcoming high school reunion, the average American man might be inclined to get a haircut. Or buy a new tie. Or undergo a spray-tan.

Jon King decided to become an Ironman.

Figuring he could stand to lose some of his recently acquired weight on the eve of his 20-year high school reunion, in 2006, King took up running in an effort to do so. Three years, four marathons and a number of triathlons later, King is a second-time competitor in the 2,000-member Kansas Ironman 70.3 triathlon, which will be held this Sunday at Clinton State Park.

“I was considerably heavier than when I left high school,” said King, a 41-year-old Lawrence lawyer. “I made the decision that I had to lose weight, and that reunion was going to be (my motivation).”

Although he had played multiple sports in high school, King’s athletic activity as an adult had been limited to low-key and occasional running. As he began to train more seriously, however, he began to see marked improvements.

Over time, he added other components to his training –namely, biking and swimming — until he had mastered them enough to begin entering local triathlons.

“It’s one of those things where you see so much improvement during the course of your training that you don’t want to let that go,” King said.

On Sunday, King is hoping the strides he’s made over the past year will be enough to turn in a quality performance — as well as erase the memories of a disappointing outcome to last June’s race.

Because of inclement weather during last year’s Ironman Kansas, King was forced to stop just over a mile from the finish line of the 70.3-mile course. The anticlimactic end marked a frustrating finish to an event he had spent months preparing for — “At that point, I had a lot of thoughts that weren’t pleasant,” he joked recently.

The disappointment was nothing, however, compared to the razzing he got from friends and training partners. Having technically fallen short of the “70.3”-mile milestone, friends say, he became the target of a good deal of jokes.

“People who run a marathon will sometimes put a ‘26.2’ sticker on their car,” said training partner Marc Scarbrough. “So I told him I was going to get him a ‘68.3’ sticker to mark his accomplishment.”

Unwilling to put up with the regular chiding — following the Ironman incident, friends had taken to calling him “Mr. 68.3” — King headed to Minneapolis two months later, completing his first (full) half-Ironman, and entering this weekend’s race, he’ll look to put last year’s disappointment behind him with a encouraging finish.

Of course, until that happens, it’s still open season on “Mr. 68.3”

“I’m really proud of him that he may finally finish his first half-Ironman in the state of Kansas,” deadpanned Scarbrough, who’ll be competing in his first Lawrence Ironman competition. “Right now, he and I have both run the same number of events here, so it’s really great that we can both complete our first race in the same year.”