Fiend (noun)

1. A devil; an evil spirit; a demon.
2. An extremely wicked or cruel person.
3. A very strong or powerful person or thing.

Origin:

From middle english feend, from old english fēond ("enemy, devil, satan"), from proto-germanic *feinþaz ("enemy, devil"), from proto-indo-european *peh₁i- ("to hate").

Examples:

1. The villagers believed that the witch was in league with fiends.
2. The fiend in human form that had so deceived her.
3. The politician was a fiend in human form, capable of great evil.
4. The fiend was a cruel and ruthless dictator who terrorized his people.
5. The fiend was a powerful and feared sorcerer who controlled the elements.