US actor Burt Young, a former boxer who earned an Oscar nomination for his breakout role as Sylvester Stallone's sidekick in the smash hit Rocky film series, has died at 83.

Stallone, who starred as the boxer Rocky Balboa in the iconic Hollywood franchise, on Wednesday hailed his “dear friend” Young as an “incredible man” and artist.

“I and the World will miss you very much...RIP,” wrote the Rocky star on Instagram.

Young's daughter, Anne Morea Steingieser, confirmed his death to The New York Times, which reported that he passed away on October 8 in Los Angeles.

Born in Queens, New York, Young spent a short time as a professional boxer before launching into acting, where he spun his grizzled, bulldog persona into a prolific career spanning over half a century.

After several small roles in television and film, including Roman Polanski's Chinatown, Young was cast as the stout sidekick Paulie in the 1976 drama Rocky written by Stallone and directed by John G. Avildsen.

In addition to the film's successful box office run, Young received an Academy Award nomination in 1977 in the Best Supporting Actor category.

Carl Weathers, who played Apollo Creed, Rocky Balboa's opponent-turned-trainer in the series, said that Young was “a beautiful and talented soul”.

He was such an integral part of the Rocky family... Paulie will be with us forever,” wrote the actor on X, formerly Twitter.