Discord is the god of chaos. He has the head of a pony and the body of... all sorts of things!

Discord's rebellion against Equestria in "Twilight's Kingdom" was actually planned by Princess Celestia from the beginning, so that the secrets of The Harmony Box could be discovered.

Discord really wants to be loved by the Ponies.

Discord was not born as a draconequus. He obtained his current form through one or multiple events in history.

The Tree of Harmony is the physical manifestation of harmony, like how Discord is with chaos.

To keep Discord in line, he is given one day out of the year to cause as much chaos as he wants. April 1st.