While we have ponies or other beings that supervise concepts like the Sun and the Moon, possibly Time and Nature, Discord oversees Chaos. But by "Chaos," Discord was meant to make things unique. Without flaws, there would be no reason for Love and Friendship. Over time, Discord became bored of Equestria, for ponies were a bit too understanding or content with the disorders of their timeline for him. Ergo, Discord brought forth more chaos (only to be sealed into a statue for thousands of years for disturbing the peace lol)