At least I'm one of many in my world, there are others like me.
[Not really the truth, there are people in similar situations, hunters that were turned vampire, but none of them are anything 'like' him. They were never a fragmentation of the twin curse. Never manipulated into ingesting the blood of several purebloods, gaining unimaginable powers. He was created specifically as a weapon to take down purebloods, he was the only one who could handle them.]
From what I've heard, having more than one slayer in your world is something of a rarity.