Ninurta

In Sumerian mythology, Ninurta was the son of Enlil and Ninhursag. Because both his parents were children of Anu (but each from a different mother), he became the second in line as heir to Anu's throne, after his father Enlil.
He was challenged in that position by Marduk, who eventually defeated him.
He was the half-brother of Nannar.