Sargent was the best portrait painter of his generation and spent most of his career wishing he were not. He called portraits 'a pimp's profession' and repeatedly tried to stop accepting commissions. The money kept pulling him back.

He was born in Florence to American expatriate parents and grew up moving between European cities. He never lived in America until he was middle-aged. He studied under Carolus-Duran in Paris, who taught him to paint directly from observation without underdrawing: load the brush, find the right tone, put it down in one stroke. The method required extraordinary hand-eye coordination and supreme confidence. Sargent had both.

Madame X, painted in 1884, nearly ended his career. The portrait of Virginie Amelie Avegno Gautreau, an American socialite in Parisian society, showed her in a black dress with one shoulder strap hanging off. The Salon audience was scandalised. Sargent repainted the strap in its proper position but the damage was done. He left Paris for London and rebuilt.

In London he became the portraitist of choice for the Anglo-American upper class. The technique is astonishing: he painted quickly, in long single-session sittings, and the brushwork has a fluency that makes other portraitists look laborious. The Wyndham Sisters, Lady Agnew of Lochnaw, and the portrait of Theodore Roosevelt show what he could do at full stretch.

He eventually did stop. After 1907 he largely abandoned portraits for watercolours and the murals at the Boston Public Library and the Museum of Fine Arts. The watercolours, painted on travels through Italy, Spain, and the Middle East, are looser and freer than the portraits and possibly better. He died in London in 1925, at sixty-nine.