Charles Henry Sims RA RWS (28 January 1873, Islington–13 April 1928, St. Boswells) was a British figurative painter known for his portraits and landscapes. He initially became renowned as a leading Edwardian painter, but following the death of his son in World War I, his work became increasingly idiosyncratic, surreal and controversial. In 1920, he was appointed Keeper, or head, of the Royal Academy Schools, a post he was eventually forced to resign in 1926. At the same time, he became estranged from his wife and children. Sims' final paintings, the Spiritual Ideas, were to some viewers his "most beautiful works," but to others highly disturbing. He committed suicide in 1928.

Born in Islington, London, Sims was the son of a costume manufacturer. An injury in infancy threatened his life and resulted in lifelong lameness in one leg. His earliest memories were of painful physiotherapy, and as a child he was unable to fully participate in physical activities. This disability was to have a profound influence on his work as an artist. As his son and biographer Alan Sims writes, "His lameness…remained always a considerable burden," and "had much to do with the peculiar direction of his art towards playful subjects and athletic technique," so that "the most notable characteristics" included "a prepossession with the swift movement of flawless bodies bathed in sunlight and air" and "a determination to escape from the actual confines of physical life into a region of his own fancy.…The charm of his happiest pictures is heightened by this pathos."

Initially apprenticed in the drapery business, at age 14 he was sent to Paris, where he learned French. Turning his back on a mercantile career, he decided to study art, and in 1890 enrolled at the South Kensington College of Art before moving back to Paris for two years at the Académie Julian. In the need of bursaries to support himself, he moved back to London and enrolled at the Royal Academy Schools in 1893, but "his Parisian insolence and cavalier ways alienated the authorities, and in 1895 he was unceremoniously expelled."

Despite the expulsion, Sims "had gained the confidence to start painting bacchanalian scenes of revelry, executed with astonishing flair," including The Vine in 1896, his first painting to be exhibited at the Royal Academy. In 1897 he exhibited Childhood, which "established his mastery of the effects of sunlight"; it was shown at the Paris Salon of 1900 and purchased by the French State (it is now at the Musée d'Orsay). He specialized in neo-classical fantasies, typically idealized scenes of women and children (and sometimes fairies and fauns) in outdoor settings. He also found success as a painter of society portraits.

In 1897, he married Agnes, a daughter of the painter John MacWhirter. She and their children, sometimes captured in photographs, would become frequent models and subjects in his paintings.

In 1906, a one-man show at the Leicester Galleries brought him critical and financial success, allowing him to relocate to rural Fittleworth and then Lodsworth, both villages near Petworth, West Sussex.

In 1907 he painted An Island Festival, "possibly his masterpiece." In 1910, The Art Journal declared him "The very Ariel of the Academy…This is the art which Keats imagined in his 'Ode on a Grecian Urn,' 'For ever panting and for ever young.'"

In 1910 he was elected a fellow of the Royal Watercolour Society, and in 1915 to the Royal Academy.