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Соловей-Разбойник (Nightingale the Robber)
http://en.wikipedia.org/wiki/Nightingale_the_Robber

http://berserk.mail.ru/cards/s-solovey-razb.jpg

Why don't you mention Кащей-бессмертный (Kaschei the immortal) and Змей Горыныч (Gorynych the serpent)? They are evil creatures but, nevertheless, very famous (or infamous) folklore characters.
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