Supreme Patriarch

The Empire's eight Colleges of Magic are eclectic and independent places of learning, where wizards are taught to use and control the Winds of Magic. The head of all the colleges is known as the Supreme Patriarch, a position of great power within the Empire. Every eight years, a wizard who has proven himself worthy can challenge the supreme patriarch in a magical duel.

Source

 * Warhammer Fantasy: Storm of Magic pg. 19