Karl Johann Kautsky (; German: ['ka?tski]; 16 October 1854 – 17 October 1938) was a Czech-Austrian philosopher, journalist, and Marxist theoretician.
Kautsky was recognized as among the most authoritative promulgators of Orthodox Marxism after the death of Friedrich Engels in 1895 until the outbreak of World War I in 1914.
Following the war, Kautsky was an outspoken critic of the Bolshevik Revolution, engaging in polemics with Vladimir Lenin, Leon Trotsky, and Joseph Stalin on the nature of the Soviet state.