This guy leads to me to believe, due to the limited information about the Everlasting Dragon elsewhere and the beginning cinematic, that the Dragons were peaceful in nature. The other four-winged dragons met in the game, Seath and the Gaping Dragon, have been driven mad or transformed, so this dragon at Ash Lake is the only seemingly sane Everlasting Dragon left. In Dark Souls, almost everything attacks us...both those that could allies depending player choices and outright enemies. And even NPCs mostly retaliate against the player if provoked. However, the Everlasting Dragon does not...even if we literally slice off his tail. Nearly all characters, monsters, etc. that do attack us/can attack us are from either the Lords/Gods or Humanity in some form or serve one of these groups or both. The Everlasting Dragon is affiliated with neither and comes from the Age of Dragons and archtrees. Combined with cinematic lines of the fire bringing "disparity," the "rebellion" against the dragons may not have been provoked by them, but rather by mortals due to our inherent lust for power, fame, fortune, and longer life. This is of course speculation and a bit of head canon, but it's a way of looking at the dynamic of the beginning of the Age of Fire as a commentary on humanity's propensity for violence and conquest over the "natural" order even if that order does not threaten us, simply to say that we control our environment, our planet. I know, I know. I'm looking way too far into it, but I like thinking about both the in-game lore and how that compares to real life situations.