Story highlights LeRoy Neiman is best known for his paintings of sports figures, especially boxers

Sylvester Stallone tapped Neiman to appear in four of his "Rocky" movies

His public persona was as almost as colorful as his artwork

Iconic American artist LeRoy Neiman, known for his trademark handlebar mustache and his bright, impressionistic portrayals of the world's top sporting events, died in New York on Wednesday. He was 91.

The cause of death was not immediately known.

"We mourn the passing of such an extraordinary and talented man," said a statement from his wife Janet and his family, who were with the artist when he died Wednesday evening at New York-Presbyterian Hospital in Manhattan.

Although his paintings captured everything from U.S. presidents to jazz musicians to the powerful animals of Africa, Neiman became best known for his bright, bold sketches of the sports world, capturing its motion and emotion in his brushstrokes.

Neiman "has the journalistic talent, as well as the artistic ability, to convey the essence of a game or contestant with great impact, from the Kentucky Derby to Wilt Chamberlain, from the America's Cup to Muhammad Ali, from the Super Bowl to Bobby Hull," sports writer Nick Seitz said.

He was named official artist of the Olympic Winter Games in Lake Placid and in Sarajevo as well as the Summer Olympics in Los Angeles.

Neiman's powerful imagery of the boxing ring, including fight posters and program covers for the historic Muhammad Ali-Joe Frazier fights, earned him a spot in the International Boxing Hall of Fame in 2007. He was so closely identified with the world of boxing that actor/director Sylvester Stallone tapped Neiman to appear in four of his "Rocky" movies.

Neiman was born June 8, 1921, in St. Paul, Minnesota, the son of Lydia Sophia Serline and Charles Julius Runquist. He later took the surname of one of his stepfathers, after his biological father abandoned the family, his biography says.

He enlisted in the army in 1942, serving during World War II. Neiman was in the invasion of Normandy and fought in the Battle of the Bulge, according to his publicist Gail Parenteau, later attending Chicago's prestigious School of the Art Institute on the G.I. Bill.

Neiman taught at the Institute for 10 years early in his career before gaining recognition as a contributing artist for Playboy in the 1950s.

The series "Man at His Leisure" appeared in the magazine for 15 years, showing the artist's impressions of sporting events and social activities. Included in the series was the Grand Prix in Monaco, the Beatles in London and the running of the bulls in Pamplona, Spain.

Staying true to his style, Neiman's public persona was as almost as colorful as his artwork.