The Inquirer is presenting one profile a day of participants in Sunday's Blue Cross Broad Street Run. See full coverage at www.philly.com/broadstreetrun.

Jonathan Lieberman calls himself a "late-bloomer Ironman triathlete" who, over the last two years, went from smoking a pack a day and weighing 241 pounds to completing the Ironman World Championship in Hawaii in October.

He wears a dog tag around his neck that never comes off, and reads "Relentless." That's one way to describe a man who signed up for his first Ironman at Lake Placid in 2010 and didn't know how to swim.

The swim in an Ironman is 2.5 miles in open water.

"I had been afraid of the water my whole life," said Jonathan, 40, a fellow in interventional radiology at Thomas Jefferson University Hospital. "But I faced my fears, bought a wet suit, and taught myself how to swim in the hospital pool after hours."

As Jonathan shed the pounds and the smokes, his health improved, but his trash-talking got only worse.

The prime target of his smack was Paul Comuso, 34, a critical-care nurse.

The doctor was all about running, biking, and swimming. The nurse was a devotee of the CrossFit craze, short, intense workouts using weights, sprints, and core exercises.

The two men had become extremely serious about getting fit, each in his own way, and agreed last May to a challenge: the Battle of Broad Street. They would race in the Broad Street Run — 10 miles, may the best man win.

Paul won by 18 seconds.

"Despite my opportunity to gloat," said Paul, "I did not. The satisfaction of finally rendering Jon speechless was the ultimate victory."

Jonathan got even more seriously into marathons and triathlons, including the famous Hawaiian Ironman in October. He befriended other Ironman competitors, including Chris Gleason, who was a big help.

Gleason, 40, died in November's Philadelphia Marathon, a quarter-mile from the finish line, where Jonathan was waiting with Gleason's family and others.

"I felt I had to do something to honor him and support his family," said Jonathan.

Jonathan and Paul agreed to a rematch this year, the second annual Battle of Broad Street, but both wanted to do it for charity. They agreed that their duel would be a fund-raiser for the G. Chris Gleason Memorial Educational Fund, to assist with future college expenses for his two children (http://fundly.com/battleofbroadstreet).

"This really hit home," said Paul. "There is a certain euphoria that one gets from helping people."

Jonathan even got commemorative key chains made and donated by Ashworth Awards, maker of Ironman awards. Anyone who donates more than $20 gets one.

"So who's it gonna be?" asks Jonathan, whose head is shaved. "Age or beauty? Bald or brunet? Speed or endurance?"

The answer comes Sunday.

Contact Michael Vitez at 215-313-3518 or mvitez@phillynews.com on Twitter @michaelvitez.