He was the son of de Montesquiou-Fezensac and his wife Pauline Duroux.
Comte Robert de Montesquiou-Fezensac was descended from the model for D'Artagnan of Dumas' The Three Musketeers and could claim most of European nobility as relatives by blood or marriage.
He is buried beside his long term partner, Gabriel Yturri (1860-1905) in the Cimetière des Gonards, Versailles, Île-de-France.
Comte Robert de Montesquiou-Fezensac was a Symbolist writer and poet, and collector. He had an important collection of far eastern art, which adorned his house and garden. Immense wealth enabled him to cultivate an aesthetic manner and his remarkable way of life inspired J.K. Huysmans' A Rebours. He was also a published poet of note and flaunted his homosexuality with enormous style.
He admired Whistler tremendously and gave Whistler an introduction into French society and his own aristocratic circle, as well as commissioning the portrait of himself, Arrangement in Black and Gold: Comte Robert de Montesquiou-Fezensac y398, which is now in the Frick Collection in New York. Whistler obviously enjoyed his company and was flattered by his attentions, and only fell out with him after hearing that the Count had sold the portrait.
He was fifteen years older than Proust, who was fascinated by him, and based the character of the Baron de Charlus on him.
Munhall, Edgar, Whistler and Montesquiou. The Butterfly and the Bat, New York, 1995 Newton, Joy, 'La Chauve-souris et le Papillon: Correspondance Montesquiou-Whistler', Nottingham French Studies, vol. 20, May 1981, pp. 30-41 ; Impressions de gris perle: Comte Robert de Montesquiou-Fezensac y397; Arrangement in Black and Gold: Comte Robert de Montesquiou-Fezensac y398.
The Correspondence of James McNeill Whistler, 1855-1903, edited by Margaret F. MacDonald, Patricia de Montfort and Nigel Thorp; including The Correspondence of Anna McNeill Whistler, 1855-1880, edited by Georgia Toutziari. Online edition, University of Glasgow 2003.