The Great Diamond Authority

"The Great Diamond Authority" is the matriarchal group of Gem leaders who rule over Homeworld and the Gem colonies.

Symbol
The symbol of the Great Diamond Authority appears on many Gem structures, but has changed over time. On structures built prior to The Rebellion, the symbol consists of four diamond shapes: one yellow, one blue, one white, and one pink. On modern structures, the pink symbol has been removed, leaving only the yellow, blue, and white shapes (now in the form of overlapping triangles), suggesting that the Authority has been reduced in membership from four to three during that time.

Yellow Diamond
One of the Diamond leaders. She is the superior of Jasper, Peridot, and many other Gems "made" for her.

Blue Diamond
One of the Diamond leaders. She was the superior of Sapphire, and many other Gems "made" for her. She was once the supervisor of the colonization of Earth.

Unknown Diamond
One of the Diamond leaders. Details about her are unknown, save for the fact that her white symbol appears alongside those representing Blue Diamond and Yellow Diamond on both ancient and modern Gem structures.

She appears to have spikey hair and her gemstone placed on her forehead.

Influence
The Great Diamond Authority has great influence on Gems of lower caste and members of their courts. Each member of a Diamond's court wears a diamond emblem on their outfit; the color of the diamond emblem worn by followers depend on the Diamond. Members of a Diamond's court are known to show respect such as Sapphire calling Blue Diamond "my Diamond". Some members are passionate and enthusiastic about working for a Diamond. For example, Peridot exclaims "I was made for Yellow Diamond!"

Unknown Diamond Gem
A former Diamond leader. Details about her are unknown other than the fact that her pink symbol that is present on ancient Gem structures.

Trivia

 * The Great Diamond Authority was yet another theory created by Ronaldo Fryman that was proven true.
 * He claimed his theory in the first season episode "Keep Beach City Weird", and Peridot confirmed the matriarchs' collective name in the second season episode "It Could've Been Great".