About Andy Warhol;
"He loved celebrities, so he painted them as well. From these beginnings he developed his later style and subjects. Instead of working on a signature subject matter, as he started out to do, he worked more and more on a signature style, slowly eliminating the hand-made from the artistic process. Warhol frequently used silk-screening; his later drawings were traced from slide projections. Warhol went from being a painter to being a designer of paintings. At the height of his fame as a painter, Warhol had several assistants who produced his silk-screen multiples, following his directions to make different versions and variations."
http://en.wikipedia.org/wiki/Andy_Warhol