Utu
is the Sun god in Sumerian mythology, the son of the moon god Nanna and the goddess Ningal

Ningal

Ningal was a goddess of reeds in the Sumerian mythology, daughter of Enki and Ningikurga and the consort of the moon god Nanna by whom she bore Utu the sun god, Inanna, and in some texts, Ishkur...

. His brother and sisters are Ishkur and Inanna

Inanna

Inanna, also spelled Inana is the Sumerian goddess of sexual love, fertility, and warfare....

 and Erishkigal.
(Inanna and Erishkigal were twins)

Utu is the god of the sun, justice, application of law, and the dispensation of the fates of the dead. He is usually depicted as wearing a horned helmet and carrying a saw-edged weapon not unlike a pruning saw. It is thought that every day, Utu emerges from a mountain in the east, symbolizing dawn, and travels either via chariot or boat across the Earth, returning to a hole in a mountain in the west, symbolizing sunset. Every night, Utu descends into the underworld to decide the fate of the dead. He is also depicted as carrying a mace, and standing with one foot on a mountain.

The sun god is only modestly mentioned in Sumerian mythology with one of the notable exceptions being the Epic of Gilgamesh

Epic of Gilgamesh

Epic of Gilgamesh is an epic poem from Mesopotamia and is among the earliest known works of literature. Scholars believe that it originated as a series of Sumerian legends and poems about the protagonist of the story, Gilgamesh king of Uruk, which were fashioned into a longer Akkadian epic much...

. In the myth, Gilgamesh

Gilgamesh

Gilgamesh was the fifth king of Uruk, modern day Iraq , placing his reign ca. 2500 BC. According to the Sumerian king list he reigned for 126 years. In the Tummal Inscription, Gilgamesh, and his son Urlugal, rebuilt the sanctuary of the goddess Ninlil, in Tummal, a sacred quarter in her city of...

 seeks to establish his name with the assistance of Utu, because of his connection with the cedar mountain

Mashu

Mashu, as described in the Epic of Gilgamesh of Mesopotamian mythology, is a great cedar mountain through which the hero-king Gilgamesh passes via a tunnel on his journey to Dilmun after leaving the Cedar Forest, a forest of ten thousand leagues span. The corresponding location in reality has been...

. Gilgamesh and his father, Lugalbanda

Lugalbanda

Lugalbanda is a character found in Sumerian mythology and literature. His name is composed of two Sumerian words meaning "young king" . Lugalbanda is listed in the postdiluvian period of the Sumerian king list as the second king of Uruk, saying he ruled for 1,200 years, and providing him with the...

 were kings of the first dynasty of Uruk

Uruk

Uruk was an ancient city of Sumer and later Babylonia, situated east of the present bed of the Euphrates river, on the ancient dry former channel of the Euphrates River, some 30 km east of modern As-Samawah, Al-Muthannā, Iraq.Uruk gave its name to the Uruk...

, a lineage that Jeffrey H. Tigay suggested could be traced back to Utu himself. He further suggested that Lugalbanda's association with the sun-god in the Old Babylonian

Old Babylonian

Old Babylonian may refer to:*the period of the First Babylonian Dynasty *the historical stage of the Akkadian language of that time...

 version of the epic strengthened "the impression that at one point in the history of the tradition the sun-god was also invoked as an ancestor".

Marduk

Marduk

Marduk was the Babylonian name of a late-generation god from ancient Mesopotamia and patron deity of the city of Babylon, who, when Babylon became the political center of the Euphrates valley in the time of Hammurabi , started to...

is spelled AMAR.UTU in Sumerian, literally, "the calf of Utu" or "the young bull of the Sun".