The Sea Tsar (Russian: Морской царь, sometimes inverted for emphasis: царь морской) is a character in East Slavic folktales and bylinas, the tsar of the sea realms.
[1] Some draw the parallel of the Sea Tsar with the tale about South Slavic morski kralj[1] recorded, e.g., by Slovenian poet and ethnologist Matija Valjavec [sl] in his 1890 collection Narodne pripovjesti u Varaždinu i okolici (Folk Tales from Varaždin and its Vicinity),[2] also published by Franc Hubad [sl] in his Pripovedke za mladino collection (referring to Valjavec).
[3] The tale in question (in both references) is called "Čudotvorni lokot" ("Magic Padlock").
It addition it turns out that the sea king also has a cat, clearly a non-maritime animal.
[3] Another sea king (morski kralj) is in the elaborate literary fairy tale Ribar Palunko i njegova žena (Palunko the Fisherman and His Wife) by Croatian writer Ivana Brlić-Mažuranić.