What folklore inspired creatures have really changed from their original versions?

[Bohandas]

I find it interesting that the myth of Koschei the Deathless seems to have been one of the inspirations for the D&D lich's phylactery, while Koschei himself became "Kostchtchie", a demon lord of frost giants, for...no good reason, other than Koschei usually being represented as a tall, evil old wizard?

He's also from a cold region of the world