Leo Tolstoy’s first name in Russian usage was Lev.
He was born Lev Nikolayevich Tolstoy. The English form “Leo” comes from the Latin equivalent of Lev, meaning “lion.” Russian references therefore usually call him Lev Tolstoy, while English-language publishing traditionally uses Leo Tolstoy.
His patronymic, Nikolayevich, means “son of Nikolai.” Russian naming conventions commonly combine a given name, patronymic, and family name, so his full Russian-style name is Lev Nikolayevich Tolstoy.
The form “Leon” can appear in some languages, but it is not the standard Russian given name used for the author. This distinction explains why biographies and Russian editions may use Lev even when English readers know him as Leo.