Who is Jack the Bookie?

Everyone is wondering about the story of Jack the Bookie, since he was mentioned don Jeopardy last night:

Who is Jack the Bookie? Clinton resident Gail Flemmons pulled out a win Thursday during her second appearance on “Jeopardy!” Flemmons was last going into “Final Jeopardy!” with $10,198. But she was the only one who knew the response to the clue: “He was also the U.S.’s best paid sports writer with stories of people like Chicago O’Brien and Jack the Bookie.” Flemmons bet it all and won with the response: “Who is Damon Runyon?” (source)

As cited, Jack the Bookie was one of the characters portrayed in Damon Runyon's stories, about salty old New Yorkers from the 19th Century. Wikipedia says "Damon Runyon spun humorous tales of gamblers, hustlers, actors, and gangsters, few of whom go by "square" names, preferring instead colorful monikers such as "Nathan Detroit," "Big Jule," "Harry the Horse," "Good Time Charley," "Jack the Bookie," or "The Seldom Seen Kid."

Who is Jack the Bookie?