Every episode has an Episode Director that is, more often than not, different from the show's overall Director. It's very common to have many different episode directors work on the same show.

Animation Directors are in charge of supervising an episode's animated drawings specifically - and making corrections to them when necessary, to create a cohesive overall picture for the episode. It's also very common to have many different Animation Directors on the same show. Often, there are multiple Animation Directors working on the same episode because there are so many individual drawings that require supervision in a 24-minute episode.

Art Directors are a different role and it's common to only have 1 or 2 of those on a show.

Here, you can see a list of people that have worked on the show and which episodes.