This concept isn't my own, though I have been using it in my campaigns. My friend Steve Bowden came up with it in his own Sertorius campaign when he felt he needed a new threat to throw at his players. He devised an elaborate cult that hunted Sertori and used their blood to make tattoos that bestowed supernatural benefits to the wearers.
Here is the Blood Cult I created based on Steve's concept for my own campaign:
From his tower near Goff-Tel, Goff-Tan has 50 soldiers under his command who are effectively part of his blood cult. He also has many cultists throughout the kingdom and an inner circle of 6 acolytes led by Nathreen. In addition he raised 4 Sertori he found as children who are loyal to him and Gesara: Rom, Ruegar, Ria and Ruga.