Qiren Lan

Lan Qiren (蓝启仁, Lán Qǐrén) is an elder of the Gusu Lan Sect known for producing outstanding students even out of the most hopeless ones. He is the uncle of Lan Xichen and Lan Wangji. Having watched his brother Qingheng-jun drive himself into self-destruction over love, he took guardianship of his nephews, teaching them strictly in an effort to prevent them from following their father's footsteps, although Lan Wangji eventually eloped with Wei Wuxian. He is hence infamously known to be a pedantic, stubborn, and strict teacher.

(Source: Wikipedia, Mo Dao Zu Shi Wikia)