Who was Baron Roman von Ungern-Sternberg and how did he gain control in Mongolia?

Baron Roman von Ungern-Sternberg, often referred to as the "Mad Baron," was a commander of tsarist cavalry units during the period of instability following the Russian Revolution of 1917.12

He gained control in Mongolia by leading his forces from eastern Siberia into the country during a time of Chinese occupation. Upon advancing on Niislel Khüree (the capital, now Ulaanbaatar), his troops successfully drove out the Chinese occupation forces. In February 1921, he restored the Bogd Khan to the throne, effectively placing the monarch under his own control.12

His subsequent rule was characterized as cruel and bloody, though it remained relatively brief. By July 1921, a Mongolian revolutionary force—supported by Soviet army units—captured the capital and established a new "people's government." The baron was captured in August 1921, handed over to Soviet authorities, and executed.12