Book: Fallen Leadership.
Archons are revered amongst the Fallen. It is unknown whether these high priests are the caretakers of the Prime Servitors, or simply vicious arbiters of the Primes' will.
Riksis collects the skulls of dead Guardians. Whether he keeps them as trophies or presents them as offerings to whatever Prime he serves, his threat is very real, and his death will bring great joy to a City in need of hope.