Although some might say that this office doesn't really merit as high a position as it possesses, that's a shortsighted view. The Master of the Challenge is quite necessary to making sure that the sept's members can cooperate smoothly. By overseeing all challenges, whether grudge matches or tests for the Rite of Accomplishment, the Master of the Challenge reinforces the sept's hierarchy; she's responsible for ensuring that all garou feel that they're being treated fairly.
The Master of the Challenge should ideally be eminently fair, but in practice she tends to reflect the attitudes and values of the sept. The Master of the Challenge of a Fenrir sept is going to be harsher and less forgiving that her counterpart in a Stargazer sept; she'll probably make sure that each challenge makes both participants stronger no matter what they want. Most Garou who fill this post are Philodox, but that's a general tendency and not a prejudice. A comprehensive knowledge of game craft is a definite requirement; plenty of combat experience is also necessary. The Master of the Challenge need not be unbeatable in all forms of challenges (and who could be?), but she must be good enough at all of them to be well versed in picking the appropriate challenge for a situation.
This position can offer a lot of fun, although it's best given to a character whose player shows a certain amount of creativity and sense of justice. A good Master of the Challenge ensures that not all challenges are physical, and that the challenge always serves the cause of sept law. This is one of the posts that can earn its holder some amount of animosity from other sept members, if they feel slighted or cheated by the character's decisions.