Exceptionally, some end in -ou, indicating the genitive case of this proper noun for patronymic reasons. Although surnames in mainland Greece are static today, dynamic and changing patronymic usage survives in middle names where the genitive of father's first name is commonly the middle name (this usage having been passed on to the Russians).
What does it mean to have the letters OU added to the ending of a males last name ?
some end in -ou, indicating the genitive case of this proper noun for patronymic reasons.