Olaudah Equiano (1745-1797) was a freed slave who became a prominent African in London, and a key figure in the British movement to end the slave trade. His autobiography, published in 1789, helped in the creation of the Slave Trade Act 1807, which ended the African trade for Britain and its colonies.
In 18th century England, a commissioned portrait of an African was a rare thing, so this painting of Olaudah, originally from Nigeria, shows the unusual status he had for that period.