Cartier-Bresson is considered one of the most influential photographers of the 20th century. He studied painting from 1922 to 1923 and his career as a photographer began in 1931. He used a 35mm Leica camera exclusively, and during the 1940s he worked for many international newspapers and magazines and together with Robert Capa, David "Chim" Seymour, and George Rodger, he founded the "Magnum" agency in 1947. In 1966 he left Magnum and in 1974, returned to painting and drawing. His thoeries on photography, including his belief in 'the decisive moment', are frequently cited.