Killing ancient dragon is pointless
winning the fight doesn't reward you with a cool ass boss weapon or fashion soul drop
he's not mechanically fun to engage
and he isn't even hostile to you in the first place. You are the one poking it with sticks.
Fighting something like this is very sisyphean.
If you want to use the
Ruler's Sword,
King's Ultra Greatsword, and/or
King's Shield, you'll need
Soul of the King. To get the Soul of the King, you need to defeat the hollowed Vendrick in the Undead Crypt. If you want to defeat the hollowed Vendrick here, you'll need
Soul of a Giant to make it actually possible to damage Vendrick, five of which needed to deal full damage and can only be gained, aside from the giant encounters and memories, also from the Ancient Dragon. Defeating Vendrick also make it possible to access the
King's Set. While you can respawn the giants down in the Black Gulch with the ascetic, it seems they only drop their loot upon their first encounter, so it's not possible to farm the soul there. Not sure if you can use the ascetic to get the soul from the memories, though.