Sir Jacob Epstein KBE (10 November 1880 – 21 August 1959) was an American and British sculptor who helped pioneer modern sculpture. He was born in the United States, and moved to Europe in 1902, becoming a British subject in 1910.

Early in his career, in 1912, The Pall Mall Gazette described Epstein as "a Sculptor in Revolt, who is in deadly conflict with the ideas of current sculpture." Revolting against ornate, pretty art, he made bold, often harsh and massive forms in bronze or stone. His sculpture is distinguished by its vigorous rough-hewn realism. Avant-garde in concept and style, his works often shocked audiences. This was not only a result of their often explicit sexual content, but also because they abandoned the conventions of classical Greek sculpture favoured by European academic critics and sculptors, to experiment instead with the aesthetics of art traditions as diverse as those of India, China, ancient Greece, West Africa, and the Pacific Islands. His larger sculptures were his most expressive and experimental, but also his most vulnerable.

Such factors may have focused disproportionate attention on certain aspects of Epstein's long and productive career, throughout which he aroused hostility, especially when violating taboos surrounding the depiction of sexuality. He often produced controversial works that challenged ideas on what was appropriate subject matter for public artworks. Epstein would often sculpt the images of friends, casual acquaintances, and even people he spotted on the street. He worked even on his dying day. He also painted; many of his watercolours and gouaches were of Epping Forest, where he lived for a time. These were often exhibited at the Leicester Galleries in London.

Bronze portrait sculpture formed one of Epstein's staple products, and perhaps the best known. These sculptures were often executed with roughly textured surfaces, expressively manipulating small surface planes and facial details.

Epstein was Jewish, and negative reviews of his work sometimes took on an antisemitic flavour, though he did not attribute the "average unfavorable criticism" of his work to antisemitism.

After Epstein died, Henry Moore wrote a tribute in The Sunday Times which included a recognition of Epstein's central role in the development of modern sculpture in Britain. "He took the brickbats, he took the insults, he faced the howls of derision with which artists since Rembrandt have learned to become familiar. And as far as sculpture in this century is concerned he took them first.... We have lost a great sculptor and a great man."

Epstein was born at 102 Hester Street on the Lower East Side of New York City. His parents were Max Epstein, formerly Jarogenski or Jarudzinski, and Mary Epstein, née Solomon, both of whom were Orthodox Jews and whose families had emigrated from Augustów in Poland. The family was middle-class, owning a number of businesses and tenements, and Jacob was the third of their eight surviving children.

As a child Epstein suffered from pleurisy and he left school aged thirteen. Between 1893 and 1898 he attended classes at the Art Students League of New York. In 1898 he organised an exhibition at the Hebrew Institute for a group of local Jewish artists and in 1899 opted to stay at Hester Street when his family moved to Madison Avenue, supporting himself by working as a tenement inspector and, briefly, as a physical education instructor. He also began selling his drawings and provided illustrations for two articles by the journalist Hutchins Hapgood. Epstein spent the winter of 1899 working as an ice-cutter with his friend Bernard Gussrow at Greenwood Lake in New Jersey.