The Thinker is originally a part of Rodin's "The Gates of Hell" (1880), but he became so enamored with it he later made a stand-alone version.
Of The Thinker, Auguste Rodin said,
What makes my Thinker think is that he thinks not only with the brain, his knitted brow, his flared nostrils, and pursed lips, but with every muscle of his arms, back and legs, with his clenched fist and gripping toes.