Latios and Natures?

[chee154]

I have a Pokemon Ruby and has caught a calm natured Latios (slateport, jump 20 times go to building to catch) for the past 3 times. I've heard mixed stories of how maybe the nature is preset... or that if you KO the Latios and beat the elite four again it sets to a different nature... I dunno... so which story is true? Or is there something else?

 

[Jenga]

I guess if you KO Latios he doesn't appear anymore.
But I don't remember when the nature is set.

 

[shookie]

The nature is set whenever any of the roamers begin roaming. Before then it's completely random, but the second they're released it's set in stone.