Artist LeRoy Neiman has died at age 91 in New York.Neiman was best known for evoking the kinetic energy of the world's biggest sporting and leisure events with bright quick strokes. He was a contributing artist at Playboy magazine for many years and was the official painter of five Olympiads.Two of Neiman's frequent subjects were the Kentucky Derby and boxing legend Muhammad Ali. Some of his racing pieces were exhibited at Churchill Downs and Neiman was among the invited guests for the grand opening of the Muhammad Ali Center in Louisville in 2005. His publicist says Neiman died Wednesday. The cause of death was not disclosed. (Information for this story also came from the Associated Press)