Friedrich Wilhelm Nietzsche (15 October 1844 – 25 August 1900) was a German philosopher, philologist, poet, cultural critic, and composer who became one of the most influential of all modern thinkers. He began his career as a classical philologist, turning to philosophy early in his academic career. In 1869, aged 24, Nietzsche became the youngest professor to hold the Chair of Classical Philology at the University of Basel. Plagued by health problems for most of his life, he resigned from the university in 1879, after which he completed much of his core writing in the following decade. In 1889, aged 44, he suffered a collapse and thereafter a complete loss of his mental faculties, with paralysis and vascular dementia. He lived his remaining years under the care of his family until his death in 1900. His works and his philosophy have fostered not only extensive scholarship, but also much popular interest and creative inspiration.

Nietzsche's work spans philosophical polemics, poetry, cultural criticism, and fiction while displaying a fondness for aphorism and irony. Prominent elements of his philosophy include his radical critique of truth in favour of perspectivism; a genealogical critique of religion and Christian morality and a related theory of master–slave morality; the aesthetic affirmation of life in response to both the "death of God" and the profound crisis of nihilism; the notion of Apollonian and Dionysian forces; and a characterisation of the human subject as the expression of competing wills, collectively understood as the will to power. He also developed influential concepts such as the Übermensch and his doctrine of eternal return. In his later work, he became increasingly preoccupied with the creative powers of the individual to overcome cultural and moral mores in pursuit of new values and aesthetic health. His body of work touched a wide range of topics, including art, philology, history, music, religion, tragedy, culture, and science, and drew inspiration from Greek tragedy as well as figures such as Zoroaster, Arthur Schopenhauer, Ralph Waldo Emerson, Richard Wagner, Fyodor Dostoevsky, and Johann Wolfgang von Goethe.

After Nietzsche’s death his sister, Elisabeth, became the curator and editor of his manuscripts. She edited his unpublished writings to fit her German ultranationalist ideology, often contradicting or obfuscating Nietzsche's stated opinions, which were explicitly opposed to antisemitism and nationalism. Through her published editions, Nietzsche's work became associated with fascism and Nazism. 20th-century scholars such as Walter Kaufmann, R. J. Hollingdale, and Georges Bataille defended Nietzsche against this interpretation, and corrected editions of his writings were soon made available. Nietzsche's thought enjoyed renewed popularity in the 1960s and his ideas have since had a profound impact on 20th- and early 21st-century thinkers across philosophy—especially in schools of continental philosophy such as existentialism, postmodernism, and post-structuralism—as well as art, literature, music, poetry, politics, and popular culture.