Marduk was the patron deity of the city of Babylon. When Babylon became the political center of the Euphrates valley in the time of Hammurabi (18th century BC), he started to slowly rise to the position of the head of the Babylonian pantheon, which he fully acquired by the second half of the second millennium BC, replacing Enlil. As the main god of the Babylonians, he was often simply called Bel ("lord").
To increase Marduk's prestige, Babylonians conflated him with many other deities, such the son of Ea and his wife Damkina (Ninhursag), Assaluhi, the god of exorcisms. Ea and Damkina were treated as Marduk's parents as well as a result. Another god conflated with him was Tishpak, sometimes assumed to be a storm deity similar to Teshub and Hadad (Baal), though seemingly regarded as an underworld god in some ancient god lists. In a myth found in Ashurbanipal's library, Tishpak battles an aquatic monster much like Marduk does in the Enuma Elish.
Marduk's own original role is obscure. In the past, some researchers assumed that much like Baal he was originally a god of agriculture and the weather, but this assumption is thought to be baseless today. In prayers, Marduk was often invoked alongside his father Ea and Shamash, the sun god. Other gods associated with him included his wife Sarpanitum and Nabu, the tutelary god of Borsippa, orignally viewed simply as Marduk's vizier. However, in later times Nabu was viewed as Marduk's and Sarpanitum's son, and even as a ruler equal to his father.
The epic poem Enuma Elish is an account of the history of Marduk's ancestors, his own birth and rise to power, as well as the creation of the world and humans. The most famous episode from it tells of Marduk's battle with the monstrous Tiamat. As a reward for his victory, Marduk received 50 names, which contain the sum of his divine powers. The motif of a god's struggle with the sea, personified as a monster, was most likely introduced to Babylon from either Anatolia or Canaan. Therefore Marduk's adversary Tiamat was possibly a derivative of earlier similar monsters, such as Yam or Illuyanka.
While most texts portray Marduk as a wise, just and heroic ruler, in the Epic of Erra he's easily tricked by Nergal, who unleashes a plague upon the streets of Babylon in his absence. However, eventually Marduk's rule is restored and Nergal's destructive talents end up harnessed against the enemies of the faithful followers of the gods. Yet another myth states that Kubaba, the only woman listed in Sumerian king lists (and possibly the model for the Hurrian goddess Kubaba, sometimes assumed to be the same as much later Cybele), was originally a mortal alewife but became a ruler thanks to her devotion to Marduk. Some legendary accounts of Sargon's life attribute his victory over the king Ur-Zababa to the latter's neglect of Marduk as well.
While the moon was associated with Nanna, the sun with Shamash and Venus with Inanna/Ishtar, Marduk's corresponding celestial body was Jupiter. His other symbols were the spade and the dragon mushussu.