Sir Sidney Robert Nolan (22 April 1917 – 28 November 1992) was one of the leading Australian artists of the 20th century. Working in a wide variety of media, his oeuvre is among the most diverse and prolific in all of modern art. He is best known for his series of paintings on legends from Australian history, most famously that of Ned Kelly, the bushranger and outlaw. Nolan's stylised depiction of Kelly's armour has become an icon of Australian art.

Sidney Nolan was born in Carlton, at that time an inner working-class suburb of Melbourne, on 22 April 1917. He was the eldest of four children. His parents, Sidney (a tram driver) and Dora, were both fifth generation Australians of Irish descent. Nolan later moved with his family to the bayside suburb of St Kilda. He attended the Brighton Road State School and then Brighton Technical School and left school aged 14. He enrolled at the Prahran Technical College (now part of Swinburne University of Technology), Department of Design and Crafts, in a course which he had already begun part-time by correspondence. In 1933, at the age of 16, he began working for Fayrefield Hats, Abbotsford, producing advertising and display stands with spray paints and dyes for six years. In 1934, he attended night classes sporadically at the National Gallery of Victoria Art School.

Nolan was a close friend of the arts patrons John and Sunday Reed, and is regarded as one of the leading figures of the so-called "Heide Circle" that also included Albert Tucker, Joy Hester, Arthur Boyd and John Perceval. Boyd and Perceval were members of the Boyd artistic family who were centred at "Open Country", Murrumbeena.

In 1938, he met and married his first wife, graphic designer Elizabeth Paterson, with whom he had a daughter, but his marriage soon broke up because of his increasing involvement with the Reeds. He joined the Angry Penguins in the 1940s, after deserting from the army during World War II; he was an editor of the Angry Penguins magazine and painted the cover for the Ern Malley edition published in June 1944. The Ern Malley hoax poems were seen by Nolan and Sunday Reed as being uncannily prescient in touching on their own personal circumstances. The Malley poems remained a real presence to him throughout his life. He painted and drew hundreds of Malley-themed works and in 1975 said it inspired him to paint his first Ned Kelly series: "It made me take the risk of putting against the Australian bush an utterly strange object."

He lived for some time at the Reeds' home, "Heide" outside Melbourne (now the Heide Museum of Modern Art). Here he painted the first of his famous, iconic "Ned Kelly" series, reportedly with input from Sunday Reed. Nolan also conducted an open affair with Sunday Reed but subsequently married John Reed's sister, Cynthia in 1948 after Sunday refused to leave her husband. He had lived in a ménage à trois with the Reeds for several years and after his marriage, he continued to see them and visited Heide at least once during their lifetimes. The years there together have been seen as a dominating factor in the subsequent lives of them all.

In November 1976, Cynthia Nolan ended her life by taking an overdose of sleeping pills in a London hotel. In 1978, Nolan married Mary Boyd (1926–2016), youngest daughter within the Boyd family and previously married to John Perceval.

Nolan painted a wide range of personal interpretations of historical and legendary figures, including explorers Burke and Wills, and Eliza Fraser. With time his paintings of Mrs Fraser came to be associated with his growing animus towards Sunday Reed. However, when first painted he was still on good terms with the Reeds and sent them photos of the works for their approval. Indeed, he gave one Fraser Island painting to Sunday Reed as a Christmas gift that year.

Probably his most famous work is a series of stylised descriptions of the bushranger Ned Kelly in the Australian bush. Nolan left the famous 1946–47 series of 27 Ned Kellys at "Heide", when he left it in emotionally charged circumstances. Although he once wrote to Sunday Reed to tell her to take what she wanted, he subsequently demanded all his works back. Sunday Reed returned 284 other paintings and drawings to Nolan, but she refused to give up the 25 remaining Kellys, partly because she saw the works as fundamental to the proposed Heide Museum of Modern Art and also, possibly, because she collaborated with Nolan on the paintings. Eventually, she gave them to the National Gallery of Australia in 1977 and this resolved the dispute. Nolan's Ned Kelly series follows the main sequence of the Kelly story. However, Nolan did not intend the series to be an authentic depiction of these events. Rather, these episodes/series became the setting for the artist's meditations upon universal themes of injustice, love and betrayal. The Kelly saga was also a way for Nolan to paint the Australian landscape in new ways, with the story giving meaning to the place.