Stanisław Ignacy Witkiewicz, commonly known as Witkacy, was a Polish writer, painter, philosopher, theorist, playwright, novelist, and photographer active before World War I and during the interwar period.

Born in Warsaw, Stanisław Ignacy Witkiewicz was a son of the painter, architect and an art critic Stanisław Witkiewicz. His mother was Maria Pietrzkiewicz Witkiewiczowa. Both of his parents were born in the Samogitian region of Lithuania. His godmother was the internationally famous actress Helena Modrzejewska.

Witkiewicz was reared at the family home in Zakopane. In accordance with his father's antipathy to the "servitude of the school," he was home-schooled and encouraged to develop his talents across a range of creative fields. Against his fathers wishes he studied at the Kraków Academy of Fine Arts with Józef Mehoffer and Jan Stanisławski.

Witkiewicz was close friends with composer Karol Szymanowski and, from childhood, with Bronisław Malinowski and Zofia Romer. Romer was romantically linked to both Bronisław Malinowski and Witkiewicz. He had a tumultuous affair with prominent actress Irena Solska who according to Anna Micińska is represented as the heroine Akne Montecalfi in his first novel, The 622 Downfalls of Bungo or The Demonic Woman, 1911. According to Micińska he also represented himself as the character Bungo and Malinowski as the Duke of Nevermore. The unfinished novel, which was not published until 1972, also describes erotic encounters between Bungo and the Duke of Nevermore. Taught wet plate photography by his father, it was during this period that he also began producing the intimate portrait photography for which he is known; producing striking portraits of his circle in Zakopane and many self-portraits.

In 1914 following a crisis in Witkiewicz's personal life due to the suicide of his fiancée Jadwiga Janczewska, for which he blamed himself, he was invited by Malinowski to act as draftsman and photographer on his anthropological expedition to the then Territory of Papua, by way of Ceylon and Australia. The venture was interrupted by the onset of World War I. After quarrelling with Malinowski in Australia, Witkiewicz who was by birth a subject of the Russian Empire, travelled to St Petersburg (then Petrograd) from Sydney and was commissioned as an officer in the Pavlovsky Regiment of the Imperial Russian Army. His ailing father, a Polish patriot, was deeply grieved by his son's decision and died in 1915 without seeing him again.

In July 1916 he was seriously wounded in the battle on Stokhid River in what is now Ukraine and was evacuated to St Petersburg where he witnessed the Russian Revolution. He claimed that he worked out his philosophical principles during an artillery barrage, and that when the Revolution broke out he was elected political commissar of his regiment. His later works would show his fear of social revolution and foreign invasion, often couched in absurdist language.

He had begun to support himself through portrait painting and continued to do so on his return to Zakopane in Poland. He soon entered into a major creative phase, setting out his principles in New Forms in Painting and Introduction to the Theory of Pure Form in the Theatre. He associated with a group of "formist" artists in the early 1920s and wrote most of his plays during this period. Of about forty plays written by Witkiewicz between 1918 and 1925, twenty-one survive, and only Jan Maciej Karol Hellcat met with any public success during the author's lifetime. The original Polish manuscript of The Crazy Locomotive was also lost; the play, back-translated from two French versions, was not published until 1962.

After 1925, and taking the name 'Witkacy', the artist ironically re-branded his portrait painting which provided his economic sustenance as The S.I. Witkiewicz Portrait Painting Company, with the tongue in cheek motto: "The customer must always be satisfied". Several of the so-called grades of portraits were offered, from the merely representational to the more expressionistic and the narcotics-assisted. Many of his paintings were annotated with mnemonics listing the drugs taken while painting a particular painting, even if this happened to be only a cup of coffee. He also varied the spelling of his name, signing himself Witkac, Witkatze, Witkacjusz, Vitkacius and Vitecasse — the last being French for "breaks quickly".

In the late 1920s he turned to novel-writing, writing two works, Farewell to Autumn and Insatiability. The latter, his major work, encompasses geopolitics, psychoactive drugs, and philosophy. In 1935 he was awarded the Golden Laurel of the Polish Academy of Literature for his novels.

During the 1930s, Witkiewicz published a text on his experiences of narcotics, including peyote, and pursued his interests in philosophy writing, Concepts and Principles Implied by the Concept of Existence 1935. He also promoted emerging writers such as Bruno Schulz.

Shortly after Poland was invaded by Germany in September 1939, Witkiewicz escaped with his young lover Czesława to the rural frontier town of Jeziory, in what was then eastern Poland. After hearing the news of the Soviet invasion of Poland on 17 September 1939, Witkacy committed suicide on 18 September by taking a drug overdose and trying to slit his wrists. He convinced Czesława to attempt suicide with him by consuming Luminal, but she survived.