Max Mermelstein (November 1, 1942 – September 12, 2008) was a drug smuggler for the Medellín Cartel in the late 70's and early 80's, who later became a key informant against the organization. In the words of James P. Walsh, Los Angeles Federal Prosecutor, "Max Mermelstein was probably the single most valuable government witness in drug matters that this country has ever known." He became a "weapon for the government."