The Thunderbird is a legendary bird which is said to be able to release lightning. This bird has not appeared as an enemy in the Castlevania series, but the Thunderbird DSS card and its associated summon spell make an appearance in Castlevania: Circle of the Moon.
In Native American mythology, the thunderbird is a legendary creature controlling the upper world while the underworld is controlled either by the underwater panther, or the Great Horned Serpent. It throws lightning at the underwater creatures and creates thunder by flapping its wings. Thunderbirds in this tradition are commonly depicted as having an X-shaped appearance.
The word "thunderbird" is also a term used in cryptozoology to describe large, bird-like creatures, generally identified with the creature said above.
- Even if it's not called "Thunderbird", the Rycuda of Castlevania: Dawn of Sorrow could be possibly a variation of this legendary creature.