8 December] 1862 – 22 March 1926) commanded the defence of the Romanian-Bulgarian border in Dobruja upon Romania's entry into World War I in August 1916.

After graduation from the Nicholas School of Military Engineering (Nikolaevskoe Inzhenernoe Uchilishche) in 1882, Zayonchkovsky served in the 5th Sapper Battalion.

He was relieved by general Dmitry Shcherbachev in April 1917 and was in retirement by the time of the October Revolution.

After the end of the Russian Civil War he switched to teaching in the Red Army Military Academy and writing.

While a professor, "Zayonchkovsky worked as an agent for the Soviet secret police at the same time he was head of the conspiratorial anti-Bolshevik Monarchist Union (The Trust).