Nikolai Konstantinovich Koltsov (Russian: Николай Константинович Кольцов; July 14, 1872 – December 2, 1940) was a Russian biologist and a pioneer of modern genetics. Among his students were Nikolay Timofeeff-Ressovsky, Vladimir Pavlovich Efroimson, A.S. Serebrovsky, and Nikolay Dubinin. Along with his students, he demonstrated the fine structure of genes, and examined the structure of the cell and pioneered the idea of a cytoskeleton. His career was cut short in Stalinist Russia due to the entanglement of Marxist ideology and interpretations that genetics was a science that supported racism, fascism and eugenics. He died unexpectedly following government persecution and there are allegations that he was executed.