Before there were Protectors there were Companions. These were Velorian Prima females, sold to the rich and powerful on seeded worlds as concubines and bodyguards because Velor had nothing else to trade for offworld technology.
The trade came about more or less by accident, and had consequences none could have imagined at the outset. If the non-human Scalantran traders had not had humans from Ishtar serving on the first ship to call at Velor, they would never have known how sexually irresistible the Velorian women were. And it wasn't until the second ship passed beyond the gold field carrying the first consignment of concubines that the women manifested their super strength and super powers -- which made them even more valuable as bodyguards.
Only many years later did it become clear that the Velorian lifespan, a mere 150 years on Velor itself, became at least three times that offworld. The Companions, as they came to be called, far outlived their formal 100-year indentures. While retaining the beauty of youth for centuries, they also gained the wisdom of age, and became valued advisors and counselers as well as lovers on their adopted worlds. Kalla Zaver'el, first of the Companions, a mere 17 when she left Velor in 1158, became the power behind the Throne on Andros, and helped guide the planet's moral and social progress from autocracy to democracy. She was eventually one of the architects of the Enlightenment.
Most Companions fell in love with the worlds where they served, and even defended or helped defend them against attacks by the nascent Arion Empire. Combat training was added to the curriculum of the Companions' Academy on Erin'lah in later years, and some of these latter-day Companions began to be called Protectors. It was a sign of times to come, although none knew it at the time.
Companions were replaced with Protectors who were further enhanced by Aphro'dite but the name change lagged behind the reality of the role by quite a lot. The Companions had been worthy of the title for quite some time before they received it.