Who is James R. Keene from Reminiscences of a Stock Operator and what is their importance?

James R. Keene is mentioned by Livingston as one of the greatest stock operators in New York near the beginning of his career. Livingston extols his virtues as a stock trader and manipulator, including his understanding of the market and the public, his ability to develop strategies, his personal integrity, his fearlessness, and the successes he scores on his clients' and his own behalf. Livingston laments that there are no records of how Keene accomplishes some of his better-known coups, as there would be a lot to learn from them.