Rosenthal was born in Chicago, Illinois, growing up in the city's West Side. As a youth, Rosenthal learned sports betting in the bleachers of Wrigley Field, and would often skip classes to attend Chicago sporting events. By the mid 1950s, he was working with the Chicago Outfit. Chosen for his gambling ability, Rosenthal ran the biggest illegal bookmaking office in the US on behalf of the Mafia. Based in Cicero, Illinois under the guise of the Cicero Home Improvement company, the Outfit and Rosenthal bought "contracts" from sports bribers to fix sporting events. After being indicted as a co-conspirator on multiple sports bribery charges, Rosenthal moved the operation to North Bay Village in Miami to avoid attention.