In The Times last Saturday, I learned for the first time of the existence of a man who is directly descended from Francis Barber, the Afro-Caribbean servant to Dr Samuel Johnson.

He is Cedric Barber, a financial advisor from Stoke-on-Trent, the great-great-great-great-grandson of the former slave.

Later in the day, I was to consider how he had cause to thank the big-hearted, altogether wonderful man whose generosity ensured the survival of the Barber family.

At a time when slavery is much on our minds, it is instructive (and uplifting) to be reminded of Johnson's philanthropy to Barber. My reminder came as I was able once more to savour the remarkable portrait of the great writer and lexicographer in Johnson is Leaving. This one-man play was written, with Bruce Purchase's special talents as a classical actor in mind, by his friend John Wain in 1994. Wain died within days of its completion. It has a special piquancy in that it is the portrait of a man who knew he was about to die written by a devoted admirer who almost certainly knew that he was as well. Did Wain share some of Johnson's thoughts about what lay ahead, and the heartbreaks, slights, failings and unkindnesses - balanced with the triumphs and successes - that were in the past? It seems very likely that he did.

Mr Purchase's performance, given in the upper library at Christ Church as part of the Oxford Literary Festival, attracted a full house. We had an afternoon in the presence of a big and generous spirit. His delivery into our company through the skills of writer and performer were never more touchingly achieved than in the passages concerning Barber, to whom Johnson generously bequeathed virtually his whole estate. "Wait till he hears that! He won't have to go and work for anyone else. He'll be able to set himself up in any modest little trade." How marvellous that he did . . .