The influential figure in the art world known for the concept of "lost generations" is Gertrude Stein. She was a prominent American writer and art collector who lived in Paris during the early 20th century. Stein's literary works, such as "Three Lives" and "Tender Buttons," often employed experimental styles and explored themes of identity and perception, resonating with the feelings of disconnection experienced by many artists and writers post-World War I. Additionally, Stein was a key figure in the Modernist movement, shaping the avant-garde art scene and influencing many renowned artists, including Pablo Picasso and Henri Matisse.