W. (Walford) Graham Robertson (1866-1948) was a gentleman artist. Born in London from a wealthy family he eventually dabbled in many forms and styles starting from Pre-Raphaelite oils to illustrations, caricatures, to portraits, later impressionistic landscapes, as well as being a talented writer. He was deeply interested in the theater and by the age of thirty had designed costumes for five major plays of which he received praise. He also painted many portraits of his friends and the leading actresses of the time.
He studied under Albert Moore (a Classical / Pre-Raphael painter 1841-1893) after first attending the South Kensington school.
Although he showed a lot of talent, he apparently never stayed with anything for very long. It seemed the art-form he was best at was the art of Schmoozing. He reveled in moving within social circles, was good friends with Burne-Jones and avidly collected Pre-Raphael art. By the time Sargent paints him as a London dandy -- he pretty much hits the nail on the head.
When John asked him why he had never painted a self-portrait, Graham responded, "Because I am not my style."
It's my impression that Graham liked to think of himself as the English equivalent of the Comte Robert de Montesquiou, whom he was also friends. Though, from what I can tell, Graham was far more talented, wielded far less influence, and didn't possess near the malicious streak (if at all) that Montesquiou had.
The painting took place in Sargent's studio and John insisted on the long fur-collared coat, jade handled cane, and Graham's own dog as props. Graham was 28 years old at the time, though the boyish face and frame made him look much younger. When Graham complained about the heat (since it was summer) Sargent persisted that the coat, itself, was the painting.
The following is an excerpt from Graham's autobiography "Time Was".