John Singer Sargent (1866 - 1925) was an American artist, considered the "leading portrait painter of his generation" for his evocation of Edwardian era luxury. During his career he created approximately 900 oil paintings and more than 2000 watercolours, as well as countless sketches and charcoal drawings. His oeuvre documents worldwide travel, from Venice to the Tyrol, Corfu, the Middle East, Montana, Maine and Florida, amongst others.
I believe Sargent first met Boldini in the summer of 1880 (Sargent was 24 and Boldini 38). John had traveled to Venice to meet his family and there he set up a studio. He very easily could have met him in Paris prior, or at the very least Sargent might have known of him. It would be in the early 80's that Boldini painted Sargent.
The names of John Singer Sargent, Boldini and Sorolla (the great Spanish master) are invariably linked when artists discuss this period. While this remarkable trio shared numerous characteristics, Boldini's work was distinguished by his slashing, rapier-like brushstrokes. Boldini was, like the other two, a consummate draftsman as well as a master painter of carefully observed tonal values. But these qualities were often overpowered by the explosive brush attack.