The art director is responsible for basically everything within the art side of a game, from the overall vision to the budget, they are the overseer, whose job it is to organise and correct. This is a creative role as to really know what is going on within the team they have to understand what there actually doing. The art director defines the principle concept of the game along with the art manager and animators (the lead in each department)
An art director needs to be and expert. The need to understand each process throughout the art department they need to be able to push the team to final goal hence being able to communicate their ideas coherently and see how all the different sections fit together.
To become an art director first and foremost a company wants experience generally with AAA titles, someone who has an in depth knowledge of each stage of development so can offer insight and advice, along with this they also need to be a good leader. Art directors can only be successful if they can see problems and do something about them.
This isn’t an easy job if something goes wrong of the game flops because of the graphics/art then it’s on the art directors head but a good art director is worth it.