Étienne Pierre Théodore Rousseau was one of the first of the French painters to be attracted to the gnarled trees, bolder-strewn hillsides and deep forests of Fontainebleau, and after visiting frequently, one of the first to move to the small nearby village of Barbizon, where he became one of the premiere painters of the Barbizon School.
After early acceptance at the critical Salon, Rousseau’s predilection for Romanticism ran afoul of the Classicists in control of the Salon at the time, and kept him from acceptance for a number of years, earning him the unenviable nickname of “le grand refusé”.
He managed to impress patrons sufficiently to carry on, however, and eventually regained acceptance, though he was consistently denied the kind of official recognition due a painter of his ability.
As a leader of the Barbizon School, his often dark and moody canvases with their roughly scumbled surfaces and open brushwork, contrasted with those in which he applied sensitive glazes, helped usher in modern styles of painting.
It would be a stretch to think of Rousseau as an actual Tonalist, but the Barbizon painters exerted considerable influence on the American painters of that style, and I see in Rousseau’s compositions — particularly those of illuminated skies seen through the framing of dark masses of foreground trees — many of the compositional conventions taken on by painters like George Inness.
Unfortunately, reproductions of Rousseau’s work on the web seem to suffer more than some of his contemporaries. The widest selection is probably at WikiArt, though the images are not large, and The Athenaeum has a decent selection. The best reproductions are probably those of the excellent collection of Rousseau’s work at the Metropolitan Museum of Art and the National Gallery, London.
You can also go to Artcyclopedia and search through the links to individual museums.
There is currently an exhibition of Rousseau’s work at the Morgan Library and Museum in NY, the first of its kind in the US. Titled “The Untamed Landscape: Théodore Rousseau and the Path to Barbizon“, it concentrates on his drawings and plein air oil sketches, forms at which Rousseau, much like Constable, excelled. The exhibition runs until January 18, 2015.
If you visit, and come out wanting to see Rousseau’s more finished work, the Met is just a cab ride away.