The Worst Witch
Mildred "Millie" Hubble is the protagonist of the series. She is a good-hearted, but bungling young witch-in-training, who never seems to get anything right. She is friends with Maud Spellbody and Enid Nightshade and has a strong rivalry with Ethel Hallow. It is Miss Hardbroom, her potions teacher, who calls her "The Worst Witch".
The Worst Witch
Miss Hardbroom is the fearsome deputy headmistress of Miss Cackle's Academy and the clear power behind the throne. She is Mildred's form mistress in first form and through various combinations of events continues to be her form mistress throughout the series. Tall, bony and sour-faced, she strikes fear into the pupils' hearts. "HB", as the girls refer to her, seems to have a particular resentment of Mildred. Miss Hardbroom frequently praises and rewards Ethel Hallow, and frequently rebukes Mildred in front of the other students. It is Miss Hardbroom who gives Mildred the title of "the worst witch in the school".