Pío Baroja y Nessi (28 December 1872 – 30 October 1956) was a Spanish writer, one of the key novelists of the Generation of '98. He was a member of an illustrious family. His brother Ricardo was a painter, writer, and engraver, and his nephew Julio Caro Baroja, son of his younger sister Carmen who was a goldsmith, was a well-known anthropologist.

Born in San Sebastián, Pío Baroja lived during almost his entire life in Madrid, where he studied Medicine. His practice as a doctor was brief, serving in Cestona, after which he returned to Madrid. There, he came into contact with Azorín and Maeztu, who inspired him to devote himself to literature, his great vocation.

He published his first books in 1900 after a series of collaborations in newspapers and magazines. This was followed by a period of intense work, which included travels throughout Spain and Europe. In 1911, he published El árbol de la ciencia. By then, he had already published, in addition to stories, articles, and essays, seventeen novels that constitute the most important part of his work.

His fame solidified, and he dedicated his life to writing, becoming increasingly sedentary. Baroja's works frequently reflect a pessimistic attitude and individualism. His political thoughts were not without ambiguities, transitioning from sympathies for anarchism in his youth, opposition to the Second Republic, and defense of a military dictatorship, yet he never abandoned his anticlericalism.