Isabel Nicholas (10 July 1912 – 27 January 1992), also known at various times as Isabel Delmer, Isabel Lambert, and Isabel Rawsthorne was a British painter, scenery and costume designer, and occasional artists' model. During the Second World War she worked in black propaganda as part of the special operations executive of the British Intelligence. She was part of an artistic bohemian society that included Jacob Epstein, Alberto Giacometti and Francis Bacon.

Isabel Nicholas was born in the East End of London, the daughter of a master mariner. She was raised in Liverpool and the Wirral. She studied at the Liverpool College of Art, won a scholarship to the Royal Academy in London and spent two years in the studio of the sculptor Jacob Epstein.

Rawsthorne's two years with Epstein and their mutual enthusiasm for Rodin developed her ideas about vitalism and movement, but she never became part of British neo-romanticism. She then moved to Paris, where she continued her studies of the nude at the liberal Académie de la Grande Chaumière. She associated with Giacometti, Tristan Tzara and the Surrealist circle, but was committed to a figurative form of modern art which she called 'Quintessentialism'. She maintained connections to an alternative circle of representational artists including Francis Gruber and Peter Rose Pulham, as well as Balthus and Derain. Her outlook was anti-idealist, intellectual and, like Giacometti, she saw painting from the real world as a challenge that could never be fully met.

Rawsthorne's work was dominated by the body, primarily paintings of figures and animals. Her father supplied exotic creatures to British zoos, and, as a child, she took to drawing these and other wildlife. Later she became interested in natural history and new ideas in Anthropology, Ecology and Ethology, such as those of her friends Michel Leiris and Georges Bataille. These inform the skeletal bird, fish and bat figures of her 1949 Hanover Gallery show, the haunting ape series, and her last, large Migration pictures.

Rawsthorne was at the heart of the Paris avant-garde and became involved with Alberto Giacometti. They shared many intellectual enthusiasms and a commitment to a modern form of representational painting. Her characteristically astonished gaze and defiant stance can be seen in the new kind of etiolated figure that Giacometti developed over the next decade.

During the Italian Campaign, she edited the magazine Il Mondo Libero.

During the 1940s, Rawsthorne adapted animal, archaic and pre-historic imagery into motifs of birth, sexuality and death. She did not share the fashionable interest in the formal properties of Oceanic or Archaic art. Instead, she investigated the uncanny 'presence' achieved by ancient figures, especially Egyptian sculpture. She also studied this quality in Early Renaissance paintings, and in the evidence of the body itself, X-rays, skeletons, figures and animals she found in the countryside or drew in London Zoo.^{[citation needed]}

From 1949, she and Bacon showcased their figurative brand of modern art at the Hanover Gallery, and she exhibited in group shows organised by the ICA and the British Council. She began a career as a designer for the Royal Ballet and the opera at Covent Garden and Sadler's Wells.