John Singer Sargent, one of the best portrait painters of the 19th century, eventually tired of his role as a society portrait painter. In his later career he greatly reduced the number of formal portrait commissions he accepted, preferring to travel and pursue his own on location watercolors.
However, he continued portraiture in a different sense, with informal portrait drawings, mostly in charcoal and many of notable figures of the time. Though Sargent drew in charcoal throughout his career, producing numerous life drawings as a student, his attention to this kind of portrait drawing was concentrated in his later years.
These drawings are remarkably fresh, loose and confident while maintaining the underlying precision of Sargent’s superb draftsmanship. The convey a range of personality, emotion and attitude on the part of the subject, and showcase Sargent’s masterful command of the most basic of all drawing media.
Unfortunately, I can’t point you directly to a trove of Sargent’s portraits drawings on the web, so I’ve gathered some scattered resources, including a couple of Google searches.
There is a nice, quite inexpensive booklet from Dover Books titled: Sargent Portrait Drawings: 42 Works by John Singer Sargent.