Dilys Derwent

Professor Dilys Derwent was a witch, who worked as a Healer at St. Mungo's Hospital for Magical Maladies and Injuries (1722-1741), and was a celebrated Headmistress of Hogwarts School of Witchcraft and Wizardry (1741-1768). Her portrait hangs not only in Dumbledore's Office along with the portraits of previous headmasters and headmistresses, but also in St. Mungo's Hospital for Magical Maladies and Injuries' main admitting area.

As a Healer and Headmistress
Derwent started working at St. Mungo's Hospital for Magical Maladies and Injuries in 1722. Derwent left the job in 1741 and became the Headmistress of Hogwarts School of Witchcraft and Wizardry that same year. She proved very popular among students and teachers, gaining her the status of one of the "most celebrated Heads" among Dumbledore and Everard. She left the post in 1768.

Attack on Arthur Weasley
When Arthur Weasley was attacked by Nagini in the Department of Mysteries in late 1995, Albus Dumbledore, then-Headmaster, asked Derwent to go to her portrait at St. Mungo's Hospital for Magical Maladies and Injuries's main admitting area in order to keep Dumbledore apprised on Mr. Weasley's condition.

Voldemort's Defeat
"All around the walls, the headmasters and headmistresses of Hogwarts were giving him a standing ovation..."

- Description

When Harry Potter went to the Headmaster's office, shortly after Lord Voldemort's defeat and the end of the Second Wizarding War, Dilys Derwent joined the ovation made by the previous Hogwarts Headmasters, sobbing unashamedly.

Etymology
The name "Dilys" means "genuine" in Welsh. Derwent may be from the name of an English lake in Cumbria, in the Lake District called "Derwent Water".

Appearances

 * Harry Potter and the Order of the Phoenix
 * Harry Potter and the Deathly Hallows