Complex sentence: He also performs (primarily in schools) in the persona of "Märchenclown Druiknui" (Druiknui, the fairy tale clown) who is the subject of one of Haasis's children's books.
Split into simpler sentences: He also performs (primarily in schools) in the persona of "Märchenclown Druiknui" (Druiknui, the fairy tale clown). Druiknui is the subject of one of Haasis's children's books.