Born Harry Stromberg in Russia, Rosen emerged as a prominent racketeer in southeast Philadelphia and, as head of the 69th Street Gang, became involved prostitution, extortion, labor racketeering and later in narcotics with Arnold Rothstein during the mid-1920s. Succeeding Max "Boo Hoo" Hoff as the city's chief bootlegger during Prohibition, he was a member of the "Big Seven" aligned with the Philadelphia faction along with Waxey Gordon and Irving Blitz, later attending the Atlantic City Conference. Rosen was one of Philly's dominant mobsters and he earned the nickname "Nig" as he once said "I was dark so they called me Nig".