Question: When did Rodin begin working on The Thinker?
About the article "The Thinker", section "Origins".

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Google honored Auguste Rodin on his 172nd birthday, featuring depicting one of his most famous sculptures, The Thinker; a bronze sculpture on marble pedestal. 
Rose Beuret and Rodin returned to Paris in 1877, moving into a small flat on the Left Bank.
Misfortune surrounded Rodin: his mother, who had wanted to see her son marry, was dead, and his father was blind and senile, cared for by Rodin's sister-in-law, Aunt Thérèse.
Rodin's eleven-year-old son Auguste, possibly developmentally delayed, was also in the ever-helpful Thérèse's care.
Rodin had essentially abandoned his son for six years, and would have a very limited relationship with him throughout his life.
Father and son now joined the couple in their flat, with Rose as caretaker.
The charges of fakery surrounding "The Age of Bronze" continued.
Rodin increasingly sought more soothing female companionship in Paris, and Rose stayed in the background.
Rodin earned his living collaborating with more established sculptors on public commissions, primarily memorials and neo-baroque architectural pieces in the style of Carpeaux.
In competitions for commissions he submitted models of Denis Diderot, Jean-Jacques Rousseau, and Lazare Carnot, all to no avail.
On his own time, he worked on studies leading to the creation of his next important work, "St. John the Baptist Preaching".
In 1880, Carrier-Belleuse – now art director of the Sèvres national porcelain factory – offered Rodin a part-time position as a designer.
The offer was in part a gesture of reconciliation, and Rodin accepted.
That part of Rodin which appreciated 18th-century tastes was aroused, and he immersed himself in designs for vases and table ornaments that brought the factory renown across Europe.
The artistic community appreciated his work in this vein, and Rodin was invited to Paris Salons by such friends as writer Léon Cladel.
During his early appearances at these social events, Rodin seemed shy; in his later years, as his fame grew, he displayed the loquaciousness and temperament for which he is better known.
French statesman Leon Gambetta expressed a desire to meet Rodin, and the sculptor impressed him when they met at a salon.
Gambetta spoke of Rodin in turn to several government ministers, likely including Edmund Turquet, the Undersecretary of the Ministry of Fine Arts, whom Rodin eventually met.
Rodin's relationship with Turquet was rewarding: through him, he won the 1880 commission to create a portal for a planned museum of decorative arts.
Rodin dedicated much of the next four decades to his elaborate "Gates of Hell", an unfinished portal for a museum that was never built.
Many of the portal's figures became sculptures in themselves, including Rodin's most famous, "The Thinker" and "The Kiss".
With the museum commission came a free studio, granting Rodin a new level of artistic freedom.
Soon, he stopped working at the porcelain factory; his income came from private commissions.
In 1883, Rodin agreed to supervise a course for sculptor Alfred Boucher in his absence, where he met the 18-year-old Camille Claudel.
The two formed a passionate but stormy relationship and influenced each other artistically.
Claudel inspired Rodin as a model for many of his figures, and she was a talented sculptor, assisting him on commissions.
Although busy with "The Gates of Hell", Rodin won other commissions.
He pursued an opportunity to create a historical monument for the town of Calais.
For a monument to French author Honoré de Balzac, Rodin was chosen in 1891.
His execution of both sculptures clashed with traditional tastes, and met with varying degrees of disapproval from the organizations that sponsored the commissions.
Still, Rodin was gaining support from diverse sources that propelled him toward fame.
In 1889, the Paris Salon invited Rodin to be a judge on its artistic jury.
Though Rodin's career was on the rise, Claudel and Beuret were becoming increasingly impatient with Rodin's "double life".
Claudel and Rodin shared an atelier at a small old castle, but Rodin refused to relinquish his ties to Beuret, his loyal companion during the lean years, and mother of his son.
During one absence, Rodin wrote to Beuret, "I think of how much you must have loved me to put up with my caprices...I remain, in all tenderness, your Rodin."
Claudel and Rodin parted in 1898.
Claudel suffered a nervous breakdown several years later and was confined to an institution by her family until her death. 
Rodin willed to the French state his studio and the right to make casts from his plasters.
Because he encouraged the edition of his sculpted work, Rodin's sculptures are represented in many public and private collections.
The Musée Rodin was founded in 1916 and opened in 1919 at the Hôtel Biron, where Rodin had lived, and it holds the largest Rodin collection, with more than 6,000 sculptures and 7,000 works on paper.
The relative ease of making reproductions has also encouraged many forgeries: a survey of expert opinion placed Rodin in the top ten most-faked artists.
Rodin fought against forgeries of his works as early as 1901, and since his death, many cases of organized, large-scale forgeries have been revealed.
A massive forgery was discovered by French authorities in the early 1990s and led to the conviction of art dealer Guy Hain.
To deal with the complexity of bronze reproduction, France has promulgated several laws since 1956 which limit reproduction to twelve casts – the maximum number that can be made from an artist's plasters and still be considered his work.
As a result of this limit, "The Burghers of Calais", for example, is found in fourteen cities.
In the market for sculpture, plagued by fakes, the value of a piece increases significantly when its provenance can be established.
A Rodin work with a verified history sold for US$4.8 million in 1999, and Rodin's bronze "Eve, grand modele – version sans rocher" sold for $18.9 million at a 2008 Christie's auction in New York.
Art critics concerned about authenticity have argued that taking a cast does not equal reproducing a Rodin sculpture – especially given the importance of surface treatment in Rodin's work.
During his lifetime, Rodin was compared to Michelangelo, and was widely recognized as the greatest artist of the era.
In the three decades following his death, his popularity waned with changing aesthetic values.
Since the 1950s, Rodin's reputation has re-ascended; he is recognized as the most important sculptor of the modern era, and has been the subject of much scholarly work.
The sense of incompletion offered by some of his sculpture, such as "The Walking Man", influenced the increasingly abstract sculptural forms of the 20th century.
Though highly honoured for his artistic accomplishments, Rodin did not spawn a significant, lasting school of followers.
His notable students included Antoine Bourdelle, Charles Despiau, the American Malvina Hoffman, and his mistress Camille Claudel, whose sculpture received praise in France.
The French order "Légion d'honneur" made him a Commander, and he received an honorary doctorate from the University of Oxford.
Rodin restored an ancient role of sculpture – to capture the physical and intellectual force of the human subject – and he freed sculpture from the repetition of traditional patterns, providing the foundation for greater experimentation in the 20th century.
His popularity is ascribed to his emotion-laden representations of ordinary men and women – to his ability to find the beauty and pathos in the human animal.
His most popular works, such as "The Kiss" and "The Thinker", are widely used outside the fine arts as symbols of human emotion and character.
To honour Rodin's artistic legacy, the Google search engine homepage displayed a Google Doodle featuring "The Thinker" to celebrate his 172nd birthday on 12 November 2012.
In 2011 the world premiere of Boris Eifman's new ballet "Rodin" took place in Saint-Petersburg, Russia.
The ballet is dedicated to the life and work of Auguste Rodin and Camille Claudel. 
The Thinker ("") is a bronze sculpture by Auguste Rodin, usually placed on a stone pedestal.
The work shows a nude male figure of over life-size sitting on a rock with his chin resting on one hand as though deep in thought, and is often used as an image to represent philosophy.
There are about 28 full size castings, in which the figure is about high, though not all were made during Rodin's lifetime and under his supervision, as well as various other versions, several in plaster, studies, and posthumous castings, in a range of sizes.
Rodin first conceived the figure as part of another work in 1880, but the first of the familiar monumental bronze castings did not appear until 1904. 
The tree was named for its proximity on campus to the copy of the eponymous statue by Auguste Rodin.