Count Lev Nikolayevich Tolstoy (Russian: Лев Никола́евич Толсто́й, also known as Leo Tolstoy, was a Russian novelist, short story writer, philosopher and playwright who primarily wrote novels and short stories. Tolstoy was a master of realistic fiction and is widely considered one of the greatest novelists of all time. He is best known for two long novels, War and Peace (1869) and Anna Karenina (1877).

Tolstoy first achieved literary acclaim in his 20s with his semi-autobiographical trilogy of novels, Childhood, Boyhood, and Youth (1852–1856) and Sevastopol Sketches (1855), based on his experiences in the Crimean War. His fiction output also includes two additional novels, dozens of short stories, and several famous novellas, including The Death of Ivan Ilyich, Family Happiness, and Hadji Murad. Later in life, he also wrote plays and essays.

Tolstoy is equally known for his complicated and paradoxical persona and for his extreme moralistic and ascetic views, which he adopted after a moral crisis and spiritual awakening in the 1870s, after which he also became noted as a moral thinker, social reformer, and Georgist. His literal interpretation of the ethical teachings of Jesus, centering on the Sermon on the Mount, caused him in later life to become a fervent Christian anarchist and anarcho-pacifist. His ideas on nonviolent resistance, expressed in such works as The Kingdom of God Is Within You, were to have a profound impact on such pivotal twentieth-century figures as Mohandas Gandhi, Martin Luther King, Jr., and James Bevel.