Many years ago, I was asked what it meant to be a Slytherin. I replied that my house was everything to me: it was- it still is.
You see, and most will not understand this, I know that Slytherin represents all the sense in the Wizarding World. Yes, Ravenclaws may be intelligent, but Slytherins are wise, and a mere ounce of wisdom is far more useful than many libraries worth of intelligence ever will be.
What I mean to say is that we Slytherins- the outcasted, the shunned, the damned, the evil, call us what you will - have seen much more than those of other houses. We must live by our wits alone, and on those we thrive.
We, unlike most Hufflepuffs, Gryffindors and – to some extent – Ravenclaws, have seen much of the world without rose-tinted glasses. My Death Eaters, the majority of whom are Slytherin – yes, there are a select few in my ranks from other houses, there is one Gryffindor, a surprising number of Hufflepuffs and numerous Ravenclaws -, know that we kill muggles because if we did not, they would kill us. We slaughter mudbloods because, when the war between our worlds is at its height, they will side with their muggle families rather than with their wizarding allies.
We kill not for some kind of sadistic pleasure, but because we must kill them in order to remain on the Earth. My cause has never been about racial purity, nor will it ever be: it is all about survival.
My goal is to conquer death; not just my own, but that of all purebloods within our world. And conquer death I will, because I am a Slytherin, the one true heir of Slytherin, and Slytherin, to me, means wisdom and survival. Slytherin, to me is everything; I am Slytherin, and yet at the same time I am not. I am Lord Voldemort.