Normally these pages are easy, because let's face it: most Pokémon have pretty obvious origins. They come from mythology, or animals, or plants, or whatever. You can whine about how the new generations have bad Pokémon all you want but Geodude is literally a rock with arms and Ekans is a snake and I don't really need to go on. And it's fine. That's Pokémon's thing and it's worked since Red and Blue.
The thing about Latias is that I have no idea what Latias is supposed to be..
I mean it looks awesome, don't get me wrong. But it doesn't really look like anything in particular. Bulbapedia says it's a cross between a jet plane and a dragon, which I can kind of see, but it's an awfully cute jet plane dragon so that tends to throw me off. Latios's dex entries do talk a lot about jet planes, so I'll take it.
However, there also exists this hilarious image of a prototype Pokémon design in which Latias was apparently fused with Blaziken:
It is, without question, the greatest thing ever. Like I love Latias and I love Blaziken but can you imagine riding around on that thing instead of Latias in Gen VI. Can you imagine..
Anyway, as for Latias's actual concept, I again had no ideas of my own, so I turned to Bulbapedia. It suggested that Latios and Latias might be based on the concept of yin and yang, given one is male and the other female, but I don't really see it; they don't really fit the concepts right. (Also, I never played Gen V, but I'm pretty sure its legendaries are supposed to be about that.) Bulbapedia also suggested the concept of aeons in Gnosticism, given that some aeons are matched male-female pairs; this seems a more likely (if loose) inspiration especially given Latias and Latios are the Eon Pokémon.