While Augustus referred to himself as the son of a god and was deified after his death, Augustus did not turn himself into a god. He is not responsible for the “divine Augustus” in his record of his deeds. Lacus Curtius says that Mommsen gave the name Res Gestae Divi Augusti to Augustus’ autobiographical Monumentum Ancyranum, and explains that the bit about Augustus being divine was a superscription by Tiberius or someone acting on his behalf. Caligula (Gaius), on the other hand, was not accepted as a god, although he did self-deify.
In ancient Babylonia, according to Marc Vab De Mieroop, kings were deified after death, as happened later in Rome, especially with the emperors. The first Babylonian king to self-deify is Naram-Sim (2254-18) whose monuments signify his divinity with a horned helmet. Naram-Sim also styled himself king of the four corners of the universe.