Riddle me this? (Fanfiction)

So Hogwarts is meant to be a safe place? Sure it is.. Only in first year the was a troll and voldemort on the back of someone's head. Second year a giant snake, man eating spiders and a possessed diary. Third year Sirius Black, need I say more? Forth year the triwirzard tournament, where a kid died and voldemort came back. And Fifth year where Dumbledores army was formed, a ghastly woman took over, who even I hate more than voldemort and Sirius black died. These are the years that I've missed thank Merlin, this year will be different, because the golden trio has never had to deal with me. So riddle me this Potter,
One of four
Bloodline pure
History and secrets
I buried them low and deep

Listened
Spoke
Disagreed
Left

If you heard me speak
You may not understand
But the last words your hear
Were my sole command

I left behind
My virtues; my beliefs
And one day
My work will be finished
Who is my descendant child?