Pyotr Semyonov-Tyan-Shansky, Russian geographer and statistician (d. 1914)
Pyotr Petrovich Semyonov or Semenov (Russian: Пётр Петрович Семёнов; 2 January (New style: 14 January), 1827 – 26 February (New style: 11 March), 1914) was a Russian geographer and statistician who managed the Russian Geographical Society for more than 40 years. He gained international fame for his pioneering exploration of the Tian Shan mountains. He was decreed to change his surname to "Semyonov of Tian Shan" (Семёнов-Тян-Шанский, Semyonov-Tyan-Shansky) at the age of 79.

Several of his descendants, including a son, Andrey Semyonov-Tyan-Shansky, and a grandson Oleg Semenov-Tian-Shansky became scientists of note.