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 English word sun derives from Proto-Germanic *sunnǭ. The Sun is sometimes referred to by its Latin name Sol or by its Greek name Helios.

Predynasty Egyptian beliefs attribute Atum as the Sun god and Horus as a god of the sky and Sun. As the Old Kingdom theocracy gained influence, early beliefs were incorporated into the expanding popularity of Ra and the Osiris-Horus mythology. Atum became Ra-Atum, the rays of the setting Sun. Osiris became the divine heir to Atum's power on Earth and passed his divine authority to his son, Horus.^{[better source needed]} Other early Egyptian myths imply that the Sun is incorporated with the lioness Sekhmet at night and is reflected in her eyes; or that the Sun is found within the cow Hathor during the night and reborn each morning as her son (bull).^{[better source needed]}

Mesopotamian Shamash played an important role during the Bronze Age, and "my Sun" was eventually used to address royalty. Similarly, South American cultures have a tradition of Sun worship as with the Incan Inti.

In Germanic mythology, the solar deity is Sol; in Vedic, Surya; and in Greek, Helios (occasionally referred to as Titan) and (sometimes) as Apollo. In Proto-Indo-European mythology the sun appears to be a multilayered figure manifested as a deity but also perceived as the eye of the sky father Dyeus.

Three theories exercised great influence on nineteenth and early twentieth century mythography. The theories were the "solar mythology" of Alvin Boyd Kuhn and Max Müller, the tree worship of Mannhardt, and the totemism of J. F. McLennan.

Müller's "solar mythology" was born from the study of Indo-European languages. Of them, Müller believed Archaic Sanskrit was the closest to the language spoken by the Aryans. Using the Sanskrit names for deities as a base, he applied Grimm's law to names for similar deities from different Indo-European groups to compare their etymological relationships to one another. In the comparison, Müller saw the similarities between the names and used these etymological similarities to explain the similarities between their roles as deities. Through the study, Müller concluded that the Sun having many different names led to the creation of multiple solar deities and their mythologies that were passed down from one group to another.

R. F. Littledale criticized the Sun myth theory, pointing out that by his own principles, Max Müller was himself only a solar myth. Alfred Lyall delivered another attack on the same theory's assumption that tribal gods and heroes, such as those of Homer, were only reflections of the Sun myth by proving that the gods of certain Rajput clans were actual warriors who founded the clans a few centuries ago, and were the ancestors of the present chieftains.

The Sun was sometimes envisioned as traveling through the sky in a boat. A prominent example is the solar barque used by Ra in ancient Egyptian mythology. The Neolithic concept of a "solar barge" (also "solar bark", "solar barque", "solar boat" and "sun boat", a mythological representation of the Sun riding in a boat) is found in the later myths of ancient Egypt, with Ra and Horus. Several Egyptian kings were buried with ships that may have been intended to symbolize the solar barque, including the Khufu ship that was buried at the foot of the Great Pyramid of Giza.