The original Grimm created by the god of discord Chaos with pieces of his soul he created them beings of immeasurble power that far surpasses any known being on remnant even the witch that dare try to control there power but the only being capable of controlling them is the god of discord for there were once apart of him created out of his will to eradicate the humans for there arrogance believing themelves to be gods and disturbing the natural order that keep the universe in check, Only some know the names of these all powerful Grimm and there purpose to keep the humans in check.
Nyx the first born daughter of Chaos and the heir of the end of the world, as the heir of the end of the world it's her duty to see that as to eradicate all life forms off the face of remnant including her descendents the mordern day Grimm, Nyx believes the natural order of the universe that all things must come to an end including herself and for those who disturbs that natural order must be eradicated immediately and without piety.
Erebus the first born son of Chaos and the sacrificial sacrifice to initiate the end of the world, although his position as a sacrifice he doesn't stay dead permanently as he was sacafriced before his entire existence ties with his sister Nyx as long she is alive he will come back from the the great beyond, although not as fanatic about the natural order as his sister he does acknowledge it since it was his purpose to help destroys those who disrupts the order that ties with the universe, Erebus doesn't acknowledge the modern day Grimm as his descendants as he believes there were born something different entirely.
Reapers many in number also the sons and daughter's of Chaos, their position are to maintaining the order of the universe and harvest the souls of those who died, born to harvest the souls of the dead and maintain order they are ruthluss to those who defy the order they will show no mercy against those they pursue, they would hunt down the witch and the wizard who tried to defy the natural order but they have bigger problems compared to those two.