Is a dark wizard. Or witch.
quiditch
Gilderoy Lockhart was the Defence Against the Dark Arts teacher in Harry Potter and the Chamber of Secrets.
One, in Defence Against the Dark Arts because of the DA
Quirinus Quirrel and Amycus Carrow (who really only taught Dark Arts). Severus Snape was one of Lord Voldemort's followers at one point but he switched sides and became a double, double agent and was working for the Order when he taught Defence Against the Dark Arts.
Dolores Umbridge.
karateka
jerome c. felisarta is great martial arts practitioner.
quiditch
The grandmaster of an art is a title usually reserved for the top ranked practitioner in any specific martial art. Each style (not each school) would have their own senior practitioner.
voldemort
Amycus Carrow, a Death Eater, is the Defence Against the Dark Arts teacher.
In the seventh book subject Dark Arts is taught by Amycus Carrow.
Dark Arts in a Long Plastic Hallway - 2009 is rated/received certificates of: Canada:14A
Gilderoy Lockhart was the Defence Against the Dark Arts teacher in Harry Potter and the Chamber of Secrets.
There is no definitive answer, as this will be a matter of opinion. All martial arts weapons are deadly in the hands of a skilled practitioner.
One, in Defence Against the Dark Arts because of the DA
From the first year it self students at Hogwarts have The Defence Against The Dark Arts subject. The depth and difficulty increases year by year.