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".
Grand High Witch
The current Witch to hold the title is a particularly powerful, evil and feared witch who hides her ancient age and disgusting ugly real looks behind an attractive disguise in order to blend in with society, and plots to wipe out all the children in England after summoning the local witches for this task. The child protagonist and his grandmother, a retired witch-hunter who once searched the world for the Grand High Witch encounter her by accident in a hotel in England, setting in motion the main plot of the novel.