Whistler is best known for his painting 'Arrangement in Grey and Black No. 1' (Whistler's Mother). He was a leading figure in the 'Art for Art's Sake' movement, arguing that painting should be about harmonious color and form rather than moral or narrative content. His book, The Gentle Art of Making Enemies, documented his famous legal battle with critic John Ruskin and his sharp wit in defense of his artistic principles. A flamboyant figure in London and Paris, his tonalist style and focus on aesthetic harmony profoundly influenced modern art and design.