What is the greek word for dark one?

There isn't one single perfect Greek word for "dark one" as the best translation depends on the nuance you want to convey. However, here are some options with slightly different connotations:

* Σκότιος (Skótios): This literally means "shadowy" or "of the shadows," and could be used to describe someone mysterious or hidden in darkness. It doesn't necessarily imply evil.

* Μέλαν (Mélan): Means "black" or "dark." You could use it as an adjective ("the mélan one") but it's less evocative of a personification than some other options.

* Νυξ (Nyx): This is the name of the primordial goddess of night. While not directly translating to "dark one," it strongly evokes darkness and could be used poetically or metaphorically.

The best choice depends heavily on the context. If you can provide more details about how you intend to use the word, I might be able to suggest a more precise translation.