Out of all the episodes in Season One, A Bird in the Hoof actually tells us more about Celestia as a character than any other episode.  And we actually learn more about her not only because of her own actions, but the actions of the pet she has chosen to spend her many years with.

DRWolf Narrator by DavionX:
http://davionx.deviantart.com/art/DrWolf-Narrator-377863090

All other Characters and Images belong to Hasbro.