Known during his lifetime as "the extraordinary Negro", Ignatius Sancho (c.1729–1780) was the first known Black Briton to vote in a British election, and the first person of African descent known to be given an obituary in the British press. As the memoir which begins this third edition of his Letters tells us, Sancho was "born A. D. 1729, onboard a ship in the Slave trade, a few days after it had quitted the coast of Guinea for the Spanish West-Indies". After "a disease of the new climate put an early period to his mother's existence; and his father defeated by the miseries of slavery by an act of suicide", Ignatius, just two years old, was brought by his master to England, and given to the man's three maiden sisters who lived in Greenwich. The sisters were far from kind, and "the petulance of their disposition" bestowed upon little Ignatius his surname, "from a fancied resemblance to the Squire of Don Quixote". Sancho would escape the grip of the sisters, when, by chance, he met the Duke of Montagu who took a liking to his "native frankness of manner". Sancho took to visiting the Duke and Duchess regularly, where he was encouraged to read, and was also lent books from the Duke's personal library. At the age of 20, shortly after the Duke's death, Sancho fled the household of the sisters to become the butler at the Montagu household, where he worked for the next two years until her death.

Immersing himself in the world of literature and music (while also working as a valet for the Duke and Duchess' daughter and husband, and then later as a greengrocer), Sancho became well known in the literary and artistic circles of the day, becoming acquainted with the likes of Thomas Gainsborough (who painted his portrait), the actor David Garrick, and the novelist Laurence Sterne. It was his correspondence with the latter which helped secure him a reputation as a man of letters, and a symbol of the abolitionist movement. At the height of the debate about slavery, in 1766, Sancho wrote to Sterne encouraging the writer to lend his fame to help lobby for the abolition of the slave trade. "That subject, handled in your striking manner," wrote Sancho, "would ease the yoke (perhaps) of many – but if only one – Gracious God! – what a feast to a benevolent heart!". Sterne's reply became an integral part of 18th-century abolitionist literature.

There is a strange coincidence, Sancho, in the little events (as well as in the great ones) of this world: for I had been writing a tender tale of the sorrows of a friendless poor negro-girl, and my eyes had scarce done smarting with it, when your letter of recommendation in behalf of so many of her brethren and sisters, came to me—but why her brethren?—or your’s, Sancho! any more than mine? It is by the finest tints, and most insensible gradations, that nature descends from the fairest face about St. James’s,1 to the sootiest complexion in Africa: at which tint of these, is it, that the ties of blood are to cease? and how many shades must we descend lower still in the scale, ’ere mercy is to vanish with them?—but ’tis no uncommon thing, my good Sancho, for one half of the world to use the other half of it like brutes, & then endeavor to make ’em so."

In another letter, writing his friend's son who had expressed racist attitudes after a visit to India, Sancho wrote:

I am sorry to observe that the practice of your country (which as a resident I love – and for its freedom – and for the many blessings I enjoy in it – shall ever have my warmest wishes, prayers and blessings); I say it is with reluctance, that I must observe your country's conduct has been uniformly wicked in the East – West-Indies – and even on the coast of Guinea. The grand object of English navigators – indeed of all Christian navigators – is money – money – money – for which I do not pretend to blame them – Commerce was meant by the goodness of the Deity to diffuse the various goods of the earth into every part—to unite mankind in the blessed chains of brotherly love – society – and mutual dependence: the enlightened Christian should diffuse the riches of the Gospel of peace – with the commodities of his respective land – Commerce attended with strict honesty – and with Religion for its companion – would be a blessing to every shore it touched at. In Africa, the poor wretched natives blessed with the most fertile and luxuriant soil- are rendered so much the more miserable for what Providence meant as a blessing: the Christians' abominable traffic for slaves and the horrid cruelty and treachery of the petty Kings encouraged by their Christian customers who carry them strong liquors to enflame their national madness – and powder – and bad fire-arms – to furnish them with the hellish means of killing and kidnapping.

In addition to his many letters — the publication of which was an immediate bestseller — Sancho also published a book for the Princess Royal about his great passion, music, and two plays.