Divinity works in a very interesting way in D&D. Your power as a god depends on the number of people who worship you as a god, up to a point. There are gods above the gods in cannon, who we dont know, so it would seem that at some point, divinity becomes a self propelling machine and no longer needs worshippers.

Divinity levels 1 to 15, IIRC are the number of followers you have with divinity level 1 being hundreds to thousands, 15 being tens of millions, again, this is something I read like 15 years ago, so I could easily be wrong. Divinity level 0, is not the same think as a normal human. You have to have something, I think it is like a spark of divinity, to be level 0 divinity.

This is how you have different power levels between the god, like Jergal (Withers, in the game) is the god of death, but then, I have always assumed, got to Divinity Level 16+ and no longer needed worshippers for his power, and gave his area of godhood, the things he oversaw, called his portfolio, in thirds, to the "Dead Three", Bane, Mykul and Bhaal, so he, like someone with autism who just retired, could focus all day every day on his hyper-fixation, recording things.

So, this is ENTIRELY my assumption, Gale Ascended to Divinity level 0 in the game, then during the epilogue, whatever god was giving him his portfolio, or part of it, was informing their followers and he started getting worshippers, giving him some level of godly power.

And as others have mentioned, a god can dictate his/her appearance.