Pavel Ivanovich Jacobi (Russian: Павел Иванович Якоби or Якобий; 15 July [O.S. 3 July] 1841, Kazan - 24 March [O.S. 11 March] 1913) was a Russian Empire revolutionary socialist, member of the Land and Liberty society, ethnographer and physician. He was a pioneer of the Pinel reforms of psychiatry in Russia, credited to be first who formulated all the principles for the new paradigm in the organizational psychiatry. One of the main ethnographic results of Jacobi at the time was discovering people of clearly Finnic descent, whom he attributed to be descendants of historical Vyatichs tribe.