'Avenger' in the Bible

That the slayer that killeth any person unawares and unwittingly may flee thither: and they shall be your refuge from the avenger of blood.

And if the avenger of blood pursue after him, then they shall not deliver the slayer up into his hand; because he smote his neighbour unwittingly, and hated him not beforetime.

These were the cities appointed for all the children of Israel, and for the stranger that sojourneth among them, that whosoever killeth any person at unawares might flee thither, and not die by the hand of the avenger of blood, until he stood before the congregation.