Born as Zelig Harry Lefkowitz, by the time he was six years old Zelig was a well-known pickpocket and thief while growing up on New York's Lower East Side as a member of Crazy Butch's pickpocket gang before joining the Eastman Gang in the late 1890s. Rising up the ranks, Zelig became leader of the Eastman Gang after "Kid Twist" (Max Zwerbach)'s death in 1908. With lieutenants Jack Sirocco and Chick Tricker, the gang had over seventy-five members, including satellite gangs such as the Lenox Avenue Gang, led by "Gyp the Blood" (aka Harry Horowitz). During this period, Zelig was also known as "The Big Yid."