Friedrich Wilhelm Nietzsche (October 15, 1844 – August 25, 1900) (German pronunciation: ) was a 19th century German philosopher and classical philologist. He wrote critical texts on religion, morality, contemporary culture, philosophy and science, using a distinctive German language style and displaying a fondness for metaphor, irony and aphorism. Nietzsche's influence remains substantial within and beyond philosophy, notably in existentialism and postmodernism. His style and radical questioning of the value and objectivity of truth have resulted in much commentary and interpretation, mostly in the continental tradition, and to a lesser extent in analytic philosophy. His key ideas include the interpretation of tragedy as an affirmation of life, an eternal recurrence (which numerous commentators have re-interpreted), a rejection of Platonism and a repudiation of both Christianity and egalitarianism (especially in the form of democracy and socialism).

Nietzsche began his career as a classical philologist before turning to philosophy. At the age of 24 he was appointed to the Chair of Classical Philology at the University of Basel (the youngest individual ever to have held this position), but resigned in 1879 because of health problems, which would plague him for most of his life. In 1889 he exhibited symptoms of insanity, living out his remaining years in the care of his mother and sister until his death in 1900.

Born on October 15, 1844, Nietzsche grew up in the small town of Röcken, near Leipzig, in the Prussian Province of Saxony. He was named after King Frederick William IV of Prussia, who turned 49 on the day of Nietzsche's birth. (Nietzsche later dropped his given middle name, "Wilhelm".) Nietzsche's parents, Carl Ludwig Nietzsche (1813–1849), a Lutheran pastor and former teacher, and Franziska Oehler (1826–1897), married in 1843, the year before their son's birth, and had two other children: a daughter, Elisabeth Förster-Nietzsche, born in 1846, and a second son, Ludwig Joseph, born in 1848. Nietzsche's father died from a brain ailment in 1849; his younger brother died in 1850. The family then moved to Naumburg, where they lived with Nietzsche's paternal grandmother and his father's two unmarried sisters. After the death of Nietzsche's grandmother in 1856, the family moved into their own house.