The title Professor is used by teachers at Hogwarts School of Witchcraft and Wizardry. It is considered rude by some to not address a member of staff as professor, Madam or Sir, as is the case with Professor Snape. Harry Potter often chose to omit this title when speaking of Snape to others, leading them to chastise him. However, the most notable exception to this is Rubeus Hagrid, who is usually referred to by his surname. The term Sir or Madam (depending on the gender) is an alternative title to use instead of Professor, on the speaker's preference. While talking to their colleagues, they usually use their first name. Professor Snape, however, preferred to use others' surnames. For example, he called Remus Lupin, Lupin, and Gilderoy Lockhart, Professor Lockhart in the Duelling Club in 1992. The exception to this would be Professor McGonagall, whom Professor Snape called Minerva.
Professors have the power to award and dock points, give detention and write notes for certain areas and activities that are usually off limits, such as the Restricted Section in the Hogwarts Library or permission to practise on the Quidditchpitch.
It is presumed that wizards and witches do not need any form of specific education, other than having received their O.W.L.s and N.E.W.T.s, to gain the title of Professor and become a Hogwarts teacher, as people such as Dolores Umbridge were able to become teachers at Hogwarts. However, even someone who did not complete their O.W.L. examinations was able to become a Professor, as long as he or she had been chosen by the Headmaster/Headmistress of the school in question, or if they had been appointed by the Ministry of Magic. This was the case with the Care of Magical Creatures Professor from 1993-1997, Rubeus Hagrid. He was expelled from Hogwarts before being able to complete any 'important' exams, however Hagrid was considered more than qualified on the subject matter. Another example was Firenze, who, as a non-wizard, had not previously attended Hogwarts.
Subjugated by Lord Voldemort after meeting him in Albania during his one-year sabbatical in 1990; attempted to steal the Philosopher's Stone; died after Voldemort abandoned him. He was replaced by an un-named Professor.
Head of Slytherin, unknown-1996. He did state to Dolores Umbridge that he had been teaching for sixteen years, just after he informed Voldemort of the Prophecy. Murdered by Voldemort during the Battle of Hogwarts.