Theurge is one of the five Auspices under which a Garou may be born. The sickle-shaped crescent moon grants the gift of insight. The Theurges are the mystics of the Garou, closer than any to the Umbra and its denizens.
Only the Ragabash start with less Rage than the Theurges do, which is just as well - many spirits avoid beings with high levels of Rage. That is the task of the Theurge - they are conduits for the spirits, explorers of the Umbra, seers and oracles. They are considered the masters of many of the powers of the Garou, including Gifts, Rites and fetishes. They are often intuitive, mysterious, secretive, and seemingly illogical, for they adhere to the ways of the spirits.
Their mind may sometimes be too deep in the realm of the spirit, and their packmates often have to ground them back in reality - Theurges are not considered to be very "practical". They are also rarely the leader of a pack, although they will often lead when in the Umbra or whenever dealing with spirits. Among their pack they are often just that - guides and sources of wisdom in the realm of the Umbra, the enactor of rites, creator of Talens and fetishes, and often must play at being a medic as well. In a battle they are more likely to serve as support compared to other Garou, but it is worth noting that even the coolest, calmest Theurges are still Garou, and burn with Rage deep within.
The most important form of Renown for those born under the crescent moon is Wisdom, with Honor as a secondary focus. Like Philodox, these two are difficult to gain quickly, and so a Theurge isn't likely to shoot up the Ranks. That said, once a Theurge is old and truly full of Wisdom, they can truly serve as an important aid to their people even if their body is not as strong as it once was, and so an old Theurge is tolerated far more than an old Ahroun, who will be expected to remove his weakness from the Garou one way or another. Sept positions that they are likely to fill include Caller of the Wyld, Keeper of the Land, and most importantly of all Master of the Rite. This is because rites are considered the natural domain of Theurges (and Philodox as well). This means they are apt to learn most any rite, although they are particularly inclined toward Mystic Rites, Caern Rites, and Seasonal Rites.
Theurges of the waxing moon are considered to interact with the spirits in a more more open, charismatic manner - they often form friendships with the spirits they serve or command. Comparitively, those of the waning moon supposedly are a darker lot, and consider spirits things to be bound, dominated, and unleashed.