The Gemma Knights are a faction in Final Fantasy Adventure and its remakes, Sword of Mana and Adventures of Mana. They are adult male members of the Mana Clan who train as warriors and are tasked with protecting the power of Mana from those who seek to abuse or deplete it.
In Sword of Mana there were 3 Gemma Knights: Cibba, Granz and Bogard.
In Secret of Mana, the Mana Knights play a role similar to the Gemma Knights.