Sadko
Sadko is a character in the Russian medieval epic Bylina. An adventurer, merchant and gusli musician from Novgorod, Sadko becomes wealthy with the help of the Sea Tsar, but is thrown in the sea when he fails to pay the Sea Tsar his due respects. This story was widely adapted in the 19th century, including in a poem by Alexei Tolstoy and an opera by Nikolai Rimsky-Korsakov.

Shown here is Sadko in the Underwater Kingdom, an 1876 painting by Ilya Repin. It depicts Sadko meeting the Sea Tsar under the sea.Painting: Ilya Repin