He had a mischievous spirit and frequently got into trouble at Hogwarts. According to his father, he usually laughed when confronted about his behavior, and had a cocky smile that everyone wanted to wipe off his face. When William landed in trouble at Hogwarts during the 2020-2021 school year, his father went to the school to talk to him in person instead of sending a Howler, since his mother thought this would be more effective. In another incident later that same school year, William ended up with no eyebrows and a "rather large" moustache after a mishap in Potions class, prompting his father to once again pay a visit to Hogwarts to talk to him.