Cognomen Doiko (Дойко 
, Doiko 
) , worldwide, is a rare last name. The family name Doiko is characteristic of Eastern Europe, particularly Bulgaria, where it is quite a rare surname, Ukraine, where it is a rare surname, and Belarus, where it is a very rare surname. Not in comparison with a country's population, it is commonest in Eastern Europe, particularly Russia, Bulgaria, and Ukraine. Likewise, Doiko is the forename as well as the last name.