In 1665 he was employed as a minor secretary on a diplomatic mission to Cleves near Brandenberg and on his return to England became part of Sir Anthony Ashley-Cooper's household at Exeter House in the Strand, as physician and confidential secretary.
John Locke c. 1672 by John Greenhill
© National Portrait Gallery, London
Sir Anthony Ashley-Cooper c. 1672-3, after John Greenhill
© National Portrait Gallery London
Three years later Locke's health, always worse in the heavily polluted London air, forced him abroad in November 1675 to winter in Montpellier. Before he left he made arrangements for his books and other belongings, including a portrait, to be cared for in Oxford and at Exeter House, not knowing that he would be abroad for over three years.
So, is this the famous portrait of Locke left in safekeeping with his colleague and friend, Shaftesbury's steward Thomas Stringer, along with his books and other effects, over which he and Mr & Mrs Stringer quarrelled when Locke asked for its return some years later?
While Locke was abroad Exeter House had the builders in in 1676 and then the Shaftesbury family and staff moved to Thanet House in Aldersgate Street and to Wimborne St Giles, the family seat. Stringer would have been dealing with all these relocations of people and goods, as well as moving to lodgings in St. Martin's Lane himself.
Locke returned to Shaftesbury's service in 1679, but then following Shaftesbury's death in disgrace in 1683, he also fled to the Netherlands for safety for the next six years. No wonder there was some confusion over the painting's ownership by 1688 when Locke asked a friend to retrieve it for him*, but this does not entirely explain Thomas Stringer's unfriendly and adamant claim that it had been a gift.
He writes to Locke's go-between, Edward Clarke in March, arguing at length:
"…wee are now too old for Children's play to have a thing given and then to have it called for againe;"
This sense of umbrage remained between both parties, and the identification of the painting remains uncertain.
John Greenhill was also a Somerset man, who trained with Peter Lely before setting up his own London studio about the time he painted this showy self portrait. It was probably intended to attract potential patrons, and he holds Lely's drawing of him like a reference.
Self Portrait, c. 1665, aged 20
© Trustees of Dulwich Gallery
By the time he painted Locke, Greenhill was an established portrait painter, but was to die young after a fall returning home from a heavy night out, in 1676. Many of his portraits of Stuart worthies are now in public collections, as are his and other artists' portraits of Locke.
*Locke wanted an engraving made for the frontispiece to his Essay concerning Human Understanding, and admitted his vanity in liking this image of his younger self.