Two weeks after the United States officially entered World War I, Irish American "Bricklayer Bill" Kennedy won the Boston Marathon wearing his stars-and-stripes bandana, rallying the crowd of patriotic spectators. Kennedy became an American hero and, with outrageous stories of his riding the rails and sleeping on pool tables, a racing legend whose name has since appeared in almost every book written on the Boston Marathon.

When journalist Patrick Kennedy and historian Lawrence Kennedy unearthed their uncle's unpublished memoir, they discovered a colorful character who lived a...