The substitute teacher is Firenze, a centaur from the Forbidden Forest.
She fires Professor Sibyll Trelawney, the Divination teacher, and she tries to fire Hagrid the groundskeeper (and Care of Magical Creatures teacher).
Emma Thompson. She will not be retuning for Deathly Hallows.
Dorles Umbridge and Snape
Sybill Trewanlyn.
No, there is no need for 'substitute teacher' to be capitalized.
Yes, both "Substitute Teacher" and "Substitute Paraprofessional" should be capitalized when referring to specific roles or job titles.
Substitute teacher.
Dolores Umbridge.
She works as a substitute teacher.
Depending on which Centaur you want, there are several named in the series. Bane, Magorian, and Ronan are all mentioned, but the one that is featured in the first movie is Firenze, I believe. In the books, he is scolded for saving Harry and later banished from the woods for betraying his kind by agreeing to help Dumbledore by replacing Trelawney as Divination teacher.
deloris umbridge the one all dressed in pink
Professor Severus Snape. Dolores Umbridge also disliked him.