|“||Knowledge or Death||”|
— Mantra of the Blade of Marmora
The Blade of Marmora is a secretive rebel group of Galran aliens fighting against the Galra Empire. They have existed for centuries infiltrating the Empire and working to end Zarkon's rule after it became clear the emperor's priorities lay in accumulation of power rather than providing stability for the good of the universe. Once Keith learns that he carries a Marmora blade and is able to activate it because of his Galran heritage, the Blade of Marmora allies with the Voltron team.
The headquarters of the Blade of Marmora is located on an asteroid beside a giant blue star that sits between two black holes, allowing the base to remain near inaccessible and completely undetected unless one has the exact coordinates. The solar flares of the star being sucked into the black holes on either side make reaching the base severely difficult, sometimes closing the base off for as long as two days. Furthermore, the gravitational pull between the black holes and the star proves tremendously dangerous: those seeking to enter the base risk either being burnt up by the star, or crushed into infinity by the black holes.
Inside, the headquarters has a main chamber and several rooms for initiates to attempt the trials to become a member, which includes intensely battling already acknowledged members. The suit given to initiates has holographic capabilities to display the wearer's deepest hopes and fears, providing a severe mental test. The Blade of Marmora has other hidden bases scattered throughout the universe, such as Communications Base Thaldycon hidden by Ulaz in the Thaldycon System by folding space-time itself using a gravity generator developed by Slav.
Kolivan is the leader of the Blade of Marmora stationed at its headquarters. Lower-ranking members, referred to as "Blades", serve as soldiers for the organization and spies tasked with infiltrating the Galra Empire at various ranks, such as Thace, who is a Galra lieutenant, and Ulaz, who was a technician before freeing Shiro. Each member dons dark armor with a mask that fully conceals their identity. They also carry a blade inscribed with the organization's emblem and made from a rare mineral known as luxite; the blades vary in form per member, but are capable of transforming from a smaller dagger design into a full-length sword. The only way this is possible is if the wielder has Galran blood. Those who are incapable of activating a blade even if they pass the organization's brutal and rigorous initiation trials are deemed unworthy of membership and owning a Marmora blade. The organization's mantra is "Knowledge or death", and Blades are so devoted to their cause of ending Zarkon's rule that they will willingly sacrifice themselves to ensure any slim chance that this goal will be realized.
- Keith is part Galran and proves that even those of mixed blood can activate the Blade of Marmora's luxite blades; his blade originally belonged to his Galran mother, Krolia.
- The Blade of Marmora emblem appears to be the emblem of the Galra Empire sliced in half.