American gangster, member of Lucky Luciano's mob family, who turned informer in 1962.

Valachi held a rank in the Mafia equivalent to that of a sergeant, with interests chiefly in the numbers rackets and other gambling from the 1930s to the '50s. In 1959 he was convicted of narcotics violations and sentenced to 15 to 20 years in prison. In June 1962, in the federal prison at Atlanta, Ga., crime boss Vito Genovese (Genovese, Vito), a fellow inmate, suspecting him (incorrectly) of having become an informer, gave him the kiss of death (a sign that he was to be killed). Valachi panicked, killed a fellow prisoner who he mistakenly thought was his assassin, and, in revenge against the death threat, told all to the U.S. Bureau of Narcotics and Dangerous Drugs, the FBI, the Justice Department, and the U.S. Senate Permanent Subcommittee on Investigations, headed by John L. McClellan. Valachi was the first syndicate member ever to describe the history, membership, and inner workings of the national crime cartel popularly called the Mafia—what Valachi termed La Cosa Nostra (“Our Thing”). Robert Kennedy called his testimony the “biggest single intelligence breakthrough yet in combating organized crime and racketeering in the United States.” Investigations, indictments, and convictions followed Valachi's testimony.

His memoirs were published as The Valachi Papers (1968), by Peter Maas.