Donald Trump says he's considering a posthumous pardon for boxing's first black heavyweight champion more than 100 years after the late Jack Johnson was convicted by all-white jury of accompanying a white woman across state lines.

The US president announced on Saturday that the actor Sylvester Stallone, a friend of his, had called to bring Johnson's story to his attention.

Johnson is a legendary figure in boxing and crossed over into popular culture decades ago with biographies, dramas and documentaries following the civil rights era.

Most famously, his story was fictionalised for the play "The Great White Hope," starring James Earl Jones, which won the Pulitzer Prize for drama and the Tony Award for best play in 1969. A film version with Jones was released in 1970.

"His trials and tribulations were great, his life complex and controversial," Mr Trump tweeted from his Mar-a-Lago club in Florida.