Task: Question Answering
Input (English): Passage: The Bertin portrait has been hugely influential. At first it served as a model for depictions of energetic and intellectual 19th-century men, and later as a more universal type. Several 1890s works closely echo its form and motifs. Jean-Joseph Benjamin-Constant's monochrome and severe 1896 Portrait of Alfred Chauchard is heavily indebted, while Léon Bonnat's stern 1892 portrait of the aging Ernest Renan has been described as a "direct citation" of Ingres' portrait.
Its influence can be seen in the dismissive stare and overwhelming physical presence of the sitter in Pablo Picasso's 1906 Portrait of Gertrude Stein. Picasso admired Ingres and referred to him throughout his career. His invoking of Bertin can be read as a humorous reference to, according to Robert Rosenblum, "Stein's ponderous bulk and sexual preference". Stein does not possess Bertin's ironic stare, but is similarly dressed in black, and leans forward in an imposing manner, the painting emphasising her "massive, monumental presence". In 1907 the Swiss artist Félix Vallotton depicted Stein, in response to Picasso, making an even more direct reference to Ingres' portrait, prompting Édouard Vuillard to exclaim, "That's Madame Bertin!"The influence continued through the 20th century. Gerald Kelly recalled Bertin when painting his restless and confined series of portraits of Ralph Vaughan Williams between 1952 and 1961. In 1975 Marcel Broodthaers produced a series of nine black and white photographs on board based on Ingres' portraits of Bertin and Mademoiselle Caroline Rivière. 
Question: What is the last name of the person whose "massive monumental presence" is emphasized in the painting?
Output (English): Stein.