Leonard (Lenny) Patrick was born on 6th October, 1913. His family emigrated to the United States and he grew up in Lincoln Park, Chicago. As a young man he became friendly with Jack Ruby and Dave Yarras.

Patrick became a member of the Chicago Outfit and during the 1930s he was imprisoned for a bank robbery in Indiana. Patrick, considered to be the prime suspect in several gangland killings, including that of Ben Zuckerman on 14th January, 1944.

In 1947 Patrick was arrested in 1947 for the murder of James M. Ragen, the national manager of the Continental Press Service, an organization that was in conflict with Mafia leader, Carlos Marcello. G. Robert Blakey and Richard Billings pointed out in their book, The Plot to Kill the President: "Four witnesses identified Lenny Patrick, Dave Yarras, and William Block as the gunmen, but after one witness was murdered, two recanted, and another fled, the indictment was dropped." Patrick was released and no charges were ever brought against him for the killing. When the Kefauver Senate Committee later investigated the murder of Ragen, something they regarded as a landmark syndicate event), another key witness in the case was murdered.

In 1955 The Chicago Tribune reported that Patrick was employed by Sam Giancana and that he was considered to be one of "two top lieutenants". During this period Patrick became the owner of a restaurant in Chicago. It has been claimed that this became the base of one of the largest bookmaking operations in the city. According to the U.S. Senate, Organized Crime and Narcotics Report (1963-64) Patrick was an "expert on gangland executions" and was credited by the police with "masterminding some of the Syndicate's most important liquidations."

The historian, David Kaiser, pointed out in The Road to Dallas (2008) that Patrick was linked to Sam Giancana: "Bugs and phone taps revealed his associations with hit men Lenny Patrick and David Yaras of Chicago (both childhood friends of Jack Ruby)." According to a FBI informant, Patrick and Dave Yarras were responsible for the killing of City Alderman, Benjamin F. Lewis on 13th February, 1963.

Lenny Patrick was interviewed by the FBI after the assassination of John F. Kennedy. He was asked about his long-time friend, Jack Ruby. Patrick acknowledged having known Ruby as "a neighborhood chum" but denied he was connected to the Mafia. Patrick claimed: "No matter how much you investigate, you'll never learn nothing, as he (Ruby) had nothing to do with nothing."

Jack Ruby's sister, Eva Rubinstein Grant, told the Warren Commission that Patrick and Dave Yarras, were two of his closest friends in Chicago. This evidence was ignored and General Counsel J. Lee Rankin told Commission members that Ruby only had links to "the minor underworld".

In a 1965 U.S. Senate report on organized crime, Patrick was identified as the "syndicate overlord of the 24th and 50th wards" whose activities included "extortion, mayhem and murders". The report went onto say that Patrick's business interests included "hotels, restaurants, supermarkets, liquor stores, aluminum products, a disposal service, vending machines, insurance and industrial uniforms". It was also pointed out that he had been arrested 28 times.

Dave Yarras was murdered in 1974. Lenny Patrick gave a deposition in 1978. He claimed he did not have any relevant information on Jack Ruby. However, he did accept that his friend, Yaras, "was closer to Ruby than he was".

In 1992, Patrick agreed to become a government witness following his indictment for racketeering charges. His testimony would result in the arrest of Gus Alex and several other key figures involved in the rackets run by the Chicago Outfit.

Leonard (Lenny) Patrick died on 1st March, 2006.