Wilhelm Mannhardt was a German mythologist and folklorist. He is known for his work on Germanic mythology, on Baltic mythology, and other pre-Christian European pantheons; and for his championing of the solar theory, namely in the early years of his career, under the influence of Jakob Grimm. Later on, Mannhardt focused more on vegetation spirits from an evolutionist point of view, namely the primitive tree cult and its later developments.

A solar deity or sun deity is a deity who represents the Sun or an aspect thereof. Such deities are usually associated with power and strength. Solar deities and Sun worship can be found throughout most of recorded history in various forms. The Sun is sometimes referred to by its Latin name Sol or by its Greek name Helios. The English word sun derives from Proto-Germanic *sunnǭ.