The Thinker was originally conceived not in heroic isolation, but as part of Rodin's monumental Gates of Hell—a pair of bronze doors intended for a museum of decorative arts in Paris. Although the doors were never cast during the sculptor's lifetime, they nevertheless provided Rodin a rich source of ideas for individual figures and groups that he worked and reworked for the rest of his career.
The theme for Gates of Hell was taken from Dante's Inferno, and this figure, planned for the lintel on top, was initially conceived as the poet himself. His nudity, though, marked him as a universal embodiment of every poet—every creator—who draws new life from the imagination. In the late 1880s Rodin began to exhibit the figure, sometimes with the title Poet, other times as Poet/Thinker. By 1896, however, it had become simply The Thinker, a still more universal image that reveals in physical terms the mental effort and even anguish of creativity. As Rodin himself described: "What makes my Thinker think is that he thinks not only with his brain, with his knitted brow, his distended nostrils and compressed lips, but with every muscle of his arms, back, and legs, with his clenched fist and gripping toes."
Rodin's Thinker exists today in many casts and sizes. More than fifty are known in this size—which is the size of Rodin's original handmade clay model.
More information on this object can be found in the Gallery publication European Sculpture of the Nineteenth Century, which is available as a free PDF https://www.nga.gov/content/dam/ngaweb/research/publications/pdfs/european-sculpture-19th-century.pdf