A lot of gods come out bragging about their enchanted weapons and super-strength, but not Nabu! Nabu doesn’t need a magic sword or a flaming whip or a quiver full of thunderbolts. You know why? Because he’s got himself a fancy pen and some tablets to write on! Oh, and a dragon named Sirrush that he rides around. Whatever, Nabu doesn’t need your approval.
Ol’ Nabu was the Assyrian god of wisdom and writing (Assyrian, Babylonian, Neo-Babylonian, Achaemenid—they all work. Ain’t nobody forgettin’ to worship Nabu). He wasn’t a fighter, but despite his pacifistic stance he was surprisingly close to the top of the pantheon-pyramid for millennia in different Mesopotamian societies due to his sacred affinity with writing. The ability to read and write, remember, was not by any means a simple gift in Nabu’s time, (a difficult-to-define expanse between 2,000 BCE and 500 CE) and as such was seen as a holy thing indeed. The stories of the gods themselves, the laws of the ruling dynasties, and the cultural histories recorded by the elite were the sole retainers of writing, and this stuff was taken seriously, as you can imagine.
Nabu, besides providing humanity with the continuing ability to write, was also the keeper of the Tablets of Destiny, wherein the fate of every living thing was recorded (similar to the role of the Greek Fates or the Germanic Norns, much later). He was a solo deity at first, but as the different cultures of Mesopotamia diffused and were aligned into more uniform empires, he was incorporated into the royal family of the presiding divinities, and became the son of the god-king Marduk. Marduk made him his official scribe and took him under his protection, and even gave Nabu his trusty dragon Sirrush to ride around on.
Nabu carried a sacred stylus, and was often depicted holding a scroll or tablet for obvious reasons (like taking the orders of the other Mesopotamian gods for sweet pizza parties, guys). Eventually, through contact with the Mediterranean societies in the later days of the Neo-Babylonian and Achaemenid dynasties, Nabu provided traits for both Apollo and Hermes, (or Mercury, still later) and as often happens, was worshipped in a wider section of the world under differing names and titles before finally being absorbed completely into the western pantheons. While he may have persisted for several centuries after the decline of the Roman empire, the arrival of Islam in Persia and Babylon would eventually stamp out the old Mesopotamian religious traditions almost completely.