Andrey Kurbsky

Prince Andrey Mikhailovich Kurbsky (1528?–1583) was a Russian political figure, military leader, and political philosopher, known as an intimate friend and then a leading political opponent of the Russian tsar Ivan the Terrible (r. 1533–1584). He defected to the Grand Duchy of Lithuania around 1564, in the midst of the Livonian War.

Kurbsky purported correspondence with tsar Ivan provides a unique source for the history of 16th-century Russia, although the attribution to Kurbsky of these letters and other works has been debated in scholarly circles since 1971.