Jimmy Burke (July 5th, 1931 – April 13th, 1996) was an associate with the Luchesse crime family, best known for being portrayed by Robert DeNiro as Jimmy Conway in the movie GoodFellas.
The reason he gets a spot here first is because he was a backstabber who looked out for himself. The movie makes Jimmy look like a good guy. In reality he was the opposite. He committed many brutal murders. Jimmy was well-known for being merciless to those he killed. In terms of brutality, he wasn't as bad as Thomas DeSimone. The main villainy of his though was the aftermath of the Lufthansa Heist, in which he ordered the mass murders of many involved, fearing their showing off could get them arrested, and thus get him implicated. But the main villainary is what he tried to do to Henry Hill and his family. Like Hill, he got involved in drugs, but much more than Henry did. This put him in tension with Paul Vario. When Hill got arrested, Burke, fearing that he would rat him out, attempted on many occassion to hurt Henry and his loved ones. The scene in GoodFellas where a Conway tries to get Karen to a back-alley, in which he claims it was to get her "dresses," is indeed based on an attempted assassination Burke tried on Karen's wife. In the movie, it was ambiguous, in real life, a murder was indeed planned.
Hill, initially reluctant to rat out his former co-associates, become more hardened against Burke, when it was revealed that he ordered an execution on Henry and his family. He is worse than DeSimone in that regard. DeSimone didn't try to backstab anyone. He let people know where he stood with them.
Burke didn't stop there. After Hill testified against him, in his jail and his deathbed (in jail) he swore that he would not stop until he had Hill and his family killed. Even Paul Vario didn't threaten Hill, according to the British documentary -- "Henry Hill: GoodFella."