Alyosha Popovich, is a folk hero of Kievan Rus', appearing in Russian folklore. He is a bogatyr and the youngest of the three main bogatyrs, the other two being Dobrynya Nikitich and Ilya Muromets. All three are represented together in Viktor Vasnetsov's famous painting Bogatyrs.
Strong bogatyr Alyosha Popovich. —From a lubok (popular print).
Bogatyrs (1898) by Viktor Vasnetsov: Alyosha Popovich is on the right.
A bogatyr or vityaz is a stock character in medieval East Slavic legends, akin to a Western European knight-errant. Bogatyrs appear mainly in Rus' epic poems—bylinas. Historically, they came into existence during the reign of Vladimir the Great as part of his elite warriors (druzhina), akin to Knights of the Round Table. Tradition describes bogatyrs as warriors of immense strength, courage and bravery, rarely using magic while fighting enemies in order to maintain the "loosely based on historical fact" aspect of bylinas. They are characterized as having resounding voices, with patriotic and religious pursuits, defending Rus' from foreign enemies and their religion. In modern Russian, the word bogatyr labels a courageous hero, an athlete or a physically strong man.
The three most famous bogatyrs, Dobrynya Nikitich, Ilya Muromets and Alyosha Popovich, appear together in Viktor Vasnetsov's 1898 painting Bogatyrs kept in the Tretyakov Gallery.
Photo of bogatyr definition from Max Vasmer's Russian Etymological Dictionary
Knight (Vityaz) at the Crossroads, Viktor Vasnetsov (1882), Russian Museum
Andrei Ryabushkin. Sadko, a rich Novgorod merchant, 1895.