Every door needs a guard. The door out of death needed three heads.
Cerberus is the hound of Hades, posted past the river Styx with the one job nobody else wanted: let the dead come in, and never, ever let them back out. Three heads so that something is always awake, a serpent for a tail, a mane of snakes. Only a handful ever slipped him. Orpheus sang him to sleep. The Sibyl drugged him with honeyed cake. Heracles simply seized all three throats and hauled him up into the daylight, the only one strong enough to take the doorman by force.
He is loyalty with the volume turned all the way up: tireless, terrible, and utterly fixed on the threshold he was given.
Snarling here at the gate, eyes lit like coals. Printed heavy on garment dyed cotton, for the ones who guard their own thresholds and let nothing past unasked.
