Jack L. Ruby was born with the name Jacob Rubenstein to Polish immigrant parents in Chicago in 1911 with various conflicting dates from March to June of that year quoted in various sources and by Ruby at various times. He had a troubled childhood and adolescence, marked by juvenile deliquency and times in foster homes. Young Ruby worked selling horse-racing tip sheets, then for a scrap-iron collectors Union; he was rumored to have minor links to organized crime. He served in the military during World War II without seeing combat. After being discharged he moved to Dallas, Texas and worked managing nightclubs, strip clubs, and dance halls, and also working as manager for entertainers.
Ruby often carried a gun with him. He suddenly came to major national attention when he shot Oswald, which he claimed was a spur of the moment action taken when the opportunity presented itself. The killing was shown live on national television, the first time such a thing happened in the United States. (Oswald was being transferred from one jail to another at the time.)
There has been much debate about Ruby's motives. He claimed that he killed Oswald in order to save Jacqueline Kennedy from testifying in a murder trial. Other people suggest that he was carrying out a Mafia "hit" (there is some evidence to support his having strong crime syndicate links), or that he was part of a conspiracy to assassinate the president and silenced Oswald to prevent him from testifying. Much suspicion is aroused by the fact that he was able to freely enter a supposedly secure area, armed with a pistol, minutes prior to the alleged assassin of the President of the United States being transferred out.
Ruby was tried and on March 14, 1964 he was convicted of Oswald's murder, but the conviction was overturned on procedural grounds. He died of cancer in prison January 3, 1967 before he could be re-tried.