marathoner
marathon runner
road runner
long-distance runner

He also became a marathon runner at the age of 60.

He has been a marathon runner since the age of 15.

So what if the kids weren't in marathon runners' shape for our first game?

The man had been a famous marathon runner in his day.

In 2009, the number of marathon runners grew to 748.

But in his youth, he had been a marathon runner.

He was one of the leading German marathon runners in the early 1990s.

You need the heart of a marathon runner to hang in.

You don't have to be a marathon runner to benefit from physical activity.

"I used to be a marathon runner in college," he said.