Pyotr Nikitich Tkachev (Russian: Пётр Ники́тич Ткачёв) (29 June 1844 – 4 January 1886) was a Russian writer, critic and revolutionary theorist who formulated many of the revolutionary principles that were later developed and put into action by Vladimir Lenin. Although Tkachev is sometimes described as "the First Bolshevik", he did not figure prominently in the mythology of the Soviet Union.