Like many Rock ‘n’ Roll Marathon Series runners, Greg Heilers is drawn to the entertainment-themed races by multiple factors. There’s the medals. (Heilers keeps his bling in a backpack so loaded down he guesses it weighs near 50 pounds.)

There’s the destination cities.

“I like to get out of town,” said the Kansas City, Mo., resident.

There’s the on-course music.

“I don’t stop to listen to (the bands),” he said, “but it is uplifting at times.”

Heilers, though, is different than most Rock ‘n’ Roll runners in one very big way. He’s a regular, with Sunday’s Humana Rock ‘n’ Roll Chicago Half Marathon representing his 100th Rock ‘n’ Roll Marathon Series event.

Asked what the century event signifies to him, the understated Heilers said, “It just means that in Dublin (next month) I get to start on the next 100.”

Heilers was raised in America’s Heartland, attending high school in Cedar Rapids, Iowa, where he ran cross country and track, plus played basketball. He ran cross country one year at Loras College in Iowa.

By 2005, he weighed 210 pounds, hardly obese at 6-feet-3. But it was heavier than he preferred, so Heilers set off on a goal to run a 5K every month for a year. He met his goal and in 2007 ran his first half marathon. (Today he weighs 185.)

Heilers ran his first Rock ‘n’ Roll event in 2008 at the inaugural San Antonio race. He’s been a regular ever since.

His favorite U.S. stop on the series: Philadelphia.

“It’s the history,” said the 48-year-old civil engineer. “The course is flat and fast.”

Heilers isn’t a dawdler, as his 3:09 marathon PR confirms. Some 33 of his Rock ‘n’ Roll races have come at the 26.2-mile distance.

Like all Rock ‘n’ Rollers, Heilers has memories banked away, stories to tell. He has built a reservoir of friends through his running travels, sharing hotel rooms, meals and tales over postrace beers.

Maybe his most indelible Rock ‘n’ Roll snapshot came in Las Vegas, the first time the race was held at night. Come about Mile 15 of the marathon, Heilers spotted a man modeling a Sacha Cohen Borat mankini, the lime green, V sling thong with straps stretched over the shoulders. The spectator had a drink in one hand, a cigarette in the other.

“It was quite the sight,” said Heilers. “It kind of throws off your marathon pace.”