1. Enoch Thompson was a real person, but they changed his name for the show. His real name was Enoch L. Johnson. Meyer Lansky and his partner Charlie "Lucky" Luciano were real people, the names used in the show are the ones they used in real life - although americanized.
2. A.R. stands for Arnold Rothstein, another real person that makes his appearance in American history - a so called mentor for the younger Lansky & Luciano.