John Decker was a bohemian character and artist working in Los Angeles in the 2nd quarter of the 20th Century. Known best as a celebrity portraitist, he also referenced Old Master paintings in his work and periodically painted landscape and still life.

Decker was born in San Francisco, CA in 1895 but spent his childhood in London. His parents left his in London at age 13, and he was there through his teens when he studied at the Slade School in London. He spent two harrowing years as a political prisoner on the Isle of Man during World War I and immigrated to America after his release.

Decker worked as a staff artist for the New York "Evening World" for a time, making caricatures for the newspaper's theatre section. He also published caricatures in other publications nation-wide.

Decker settled in Los Angeles and opened a studio in Hollywood that was frequented by celebrities having their portraits painted. The Mark brothers, Errol Flynn, Greta Garbo, Mickey Rooney, John Barrymore, W.C. Fields, Charlie Chaplin and many others sat for portraits, often painted in Old Master styles or directly referencing Old Master paintings of note.

In this time period, Decker had one-person exhibitions in Rome and around Los Angeles. He showed at Los Angeles County Museum of Art (1942-1944); the Virginia Museum (1944); The deYoung Museum (1946) and the Art Institute of Chicago. In some shows, Decker's work was displayed alongside the works of actual Old Master painters, and inexplicably to viewers today, they were sometimes mistaken for old pieces from the Renaissance period. Decker also painted works for Hollywood productions sets and in 1944, was a partner with actor Errol Flynn in the Decker-Flynn Gallery, Hollywood. Decker was known for throwing wild parties and for an eccentric personality. He died in Los Angeles in 1947 of cirrhosis of the liver.