The one who designs costumes, usually in the theatre or in film.
The Costume Designer has one of the most important jobs of them all, because the actors would look (even more) stupid without them.
Before any of the actors do, the costume designer gets the script and does renderings-drawings of what they think would look good on the actors.
When the show is cast, the costume designer starts busting their ass. She or He finds costumes that exsist in the theatre department of wherever they're working, and whatever they can't find has to be made or bought. And then when they think all their work is done, the director decides to change it, and then they have a fucking nervous breakdown---
The costume designer usually has a crew, because, you know, they can't do everything by themselves. Even though it ends up working that way...
This crew is split in two parts: The Running Crew and The Designing Crew.
The Running Crew does quick changes (they are what they sound like) and brings the costumes down in the show closet for the show. This can be really hard if there is 30 characters and 6 people in a show, for example.
The Designing crew are like mini-costume designers, just not as good.
Be nice to your Costume Designer, for they can make or break you...and themselves. So just be nice.