John L. Parker, Jr. is the writer of the cult classic Once A Runner and a more recently published Again to Carthage. Both books feature the struggles Quenton Cassidy deals with in his running career.

Cassidy, a passionate, obsessive runner, is first introduced in Once A Runner, published in 1978. Thirty years later Parker follows the career of Cassidy in a second book Again to Carthage, published in late 2007. In "Once a Runner" Cassidy is an elite college athlete who is suspended from school and prohibited from competing in his university's track meets. He trains in private hoping to compete in disguise. In "Again to Carthage," ten years have passed for Cassidy. After taking a break from running, he begins training again in earnest trying to recapture the feeling and the glory of the past, this time through long distance running.