For 70 years staff have not known the identity of a black man in chains, dressed in red, who appears in an imposing painting in the entrance to Wilberforce's home in Hull.

But art experts from the US have now identified him as one of the greatest 19th century Shakespearian actors, Ira Aldridge.

An American stage actor who made his career largely on the London stage, Aldridge was born in 1807, the year the slave trade was abolished in the British Empire.

He faced a largely hostile press, because of his colour, and became an outspoken abolitionist, but also won plaudits for his performances, A Hull paper describing his Othello as "such as can be equalled by very few actors of the present day."

The Chicago Art Institute found Wilberforce's painting on a database on the internet when researching the original by the artist John Simpson, which hangs alongside paintings by Monet and Cezanne. The artwork that hangs in Wilberforce House is a copy.

Keeper of Social History at Wilberforce House Museum Vanessa Salter said: "The mystery of who the subject in the print has finally been solved and we are very excited to find the missing piece of the jigsaw puzzle.

"We knew the painting was important, but we had no idea that it depicted one of the greatest Shakespearian actors of the 19th century."