knights..the dark ones? possibly..

• originally known as Knights of Walpurgis
• founded possibly in the 1950s
• Headquarters- initially a House, later on a Manor
• prominent members- 12-14
• typical attire- black hooded robes, and masks
• founder's name literally translates to 'flight of death'

who?
it is the Death Eaters. praveen gatt'a'i gets this right, and so do a couple of others who texted me the answer.