Jack Ruby, in full Jack L. Ruby, original name Jacob Rubenstein, (born March 25?, 1911, Chicago, Illinois, U.S.—died January 3, 1967, Dallas, Texas), American nightclub owner who killed Lee Harvey Oswald, the suspected assassin of Pres. John F. Kennedy, on November 24, 1963, as Oswald was being transferred to a county jail. Despite Ruby’s claims to the contrary—and a lack of evidence—some have posited that he was part of a larger conspiracy concerning Kennedy’s assassination.

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Born Jacob Rubenstein, he used different variations of that name before eventually settling on Jack Ruby. His birth date is uncertain, though he typically used March 25, 1911. He was born to Polish immigrants and was raised in the Jewish faith; he later became violent in the face of anti-Semitism. His parents separated when he about 10 years old, and his already turbulent home life became increasingly unstable. The following year, he was sent to the Institute for Juvenile Research because of his failure to attend school and for being “incorrigible at home.” By that time he had earned the nickname “Sparky,” which was widely believed to be a reference to his volatile temper. The institute found his mother to be unfit to care for him—she was later committed to a state hospital on two occasions—and recommended that he be moved to a different home. According to reports, a juvenile court placed Ruby with foster parents in 1923, but he was returned to his mother’s care the following year. However, Ruby claimed that he was in foster homes for four or five years. It is believed that he left school when he was about 16. Ruby subsequently held various odd jobs, including ticket scalper.

Ruby moved to California in about 1933 but apparently returned to Chicago four years later. His employment continued to be varied. After serving as a union organizer, he sold punchboard gambling devices as well as plaques commemorating the attack on Pearl Harbor. During World War II, he served (1943–46) in the U.S. Army Air Forces. In 1947 Ruby moved to Dallas to help run the Singapore Supper Club (later called the Silver Spur Club), which was owned by one of his sisters. That year he also legally changed his name to Jack L. Ruby. He subsequently became involved in other nightclub operations and had varying degrees of success. One of his more lasting ventures was the Vegas Club, of which he became sole owner in 1954. During this period, Ruby engaged in numerous violent incidents, which often involved employees and club patrons. In addition, he was arrested for a number of minor offenses, such as carrying a concealed weapon, though he was never convicted of a crime. Through these legal run-ins and his various clubs, Ruby met, and allegedly befriended, a number of police officers.

On November 22, 1963, President John F. Kennedy was fatally shot during a motorcade in Dallas. According to reports, Ruby was deeply upset by the assassination, and he attended the press conference that was held following the arrest of Lee Harvey Oswald. On November 24 Ruby went to a Western Union office in order to wire money to an exotic dancer who worked at one of his clubs. Immediately thereafter he walked to Dallas City Hall, where Oswald was being transferred to the county jail. Ruby entered the basement area, which was filled with police officers and media members. As Oswald was led out, Ruby shot him in the stomach at close range before being restrained. The event was captured live on television.

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Ruby claimed that he killed Oswald in order to spare Jacqueline Kennedy from having to testify at Oswald’s trial. Ruby’s own trial began in February 1964, and his defense attorney, Melvin Belli, argued that he had been temporarily insane when he shot Oswald. The following month, however, a jury found Ruby guilty of murder with malice, and he received the death penalty. Ruby appealed, and in October 1966 a Texas court overturned the conviction, ruling that illegal testimony had been allowed at his trial. Before a new trial could be held, however, Ruby died from a pulmonary embolism shortly after being diagnosed with cancer.

Although Ruby always maintained that he had acted alone—a statement supported by the subsequent Warren Commission—some speculated that he was part of a larger conspiracy and that he had killed Oswald to keep him from talking. Such theorists often pointed to Ruby’s alleged ties to organized crime. The Warren Commission, however, found that, while some of his ventures were “shady,” Ruby had no deep involvement in the crime world.