Tamara Platonovna Karsavina (1885-1978)
one of the great Russian ballet dancers. She first made her mark with the internationally acclaimed Ballets Russes of Serge Diaghilev and was a true prima ballerina -- intelligent and gifted.
By 1912 (possibly 1911 as well based on Harvard dating) at the age of 27, she was performing in Paris in the lead role in "Thamar". The ballet was set in the exotic Caucasian land of Georgia. The Queen Thamar would lure an innocent man to her castle, dance with her victim before finally stabbing him to death. 
Tamara's costume, along with the set, were both designed by the then new-international-sensation Léon Bakst, whom had himself, only a couple or years prior (1910), burst onto the Paris theater scene with the production of the ballet Schéhérazade. The staging was so brilliant in its color and design that these productions (Thamar followed in this same theme) were declared "visual masterpieces" by the public and critics.
The lure, for Sargent, to
the leading dancer wearing her costume must have been tremendous. As he
had done with the Javanese
Dancers, Ellen Terry
Lady Macbeth, and others, these thematic works combined John's love
of the exotic, beautiful costumes, and the art of portraiture.
She stayed in Russia during the Russian Revolution (1917) but by 1919, when she married her husband Henry J. Bruce (a British diplomat) they fled breifly to London, only to return later that year.
Tamara Karsavina was
for many years with Great Britains' Royal Academy of Dancing,
the time it received its charter in 1936.
A bill of
sale in curatorial file. Drawing was sold to Grenville Winthrop for
$1500. Scott and Fowles number from back of frame: 5981. Scott and
Fowles bill lists title as: "Portrait of 'Karsavina' the Russian