Yep, the great and mighty Bahamut, the paragon of good dragons all across the cosmos, was originally a darn big fish.
Oh well, we can still work with this.
When I was reimagining Tiamat, I went back to her roots a little to dredge up some of that old stuff and put it into use. Naturally, in keeping with my idea of dualities as a part of the setting of Therafim, she had to have a male counterpart, her greatest lover as well as her greatest enemy, the father of the gods just as she was the mother. When I tried to do the same with Bahamut, I discovered he was the Arabic divine fish on which much of the weight of the cosmos rested. He's a holy fish of ginormous proportions, sure, but he's still a fish.
Aw, nuts with it, or so I thought to myself: Bahamut's been in pretty much every Final Fantasy, for goodness sake. He's as classic D&D as they come, too. And I've already got an idea for a serpent (Worm, actually) gnawing at the base of reality, just like in the Arabic cosmos (see http://en.wikipedia.org/wiki/Falak for more on that), so what if I replace the fishy with a dragon instead. I've never really been that good with picking out cool names anyway, so Bahamut was as good as any, and you can't buy that kind of roleplaying lore anyway.
So, this is Therafim's version of Bahamut. He's not the same as Bahamut in most other settings, and some of his differences are pretty extreme, just the same as with Tiamat, his evil counterpart. But he's still recognizable as the king of good dragons, just like Tiamat is the queen of evil dragons, and they're both pretty hot stuff. I think I've done them proper justice, even while making changes to fit the setting more perfectly, and hope that the overall effect works for others.