The Great Diamond Authority

"Each Gem is made with a purpose: To serve the order of the Diamonds. Those who cannot fit inside this order must be purged."

The Great Diamond Authority is the matriarchal body of Gem leaders who rule in absolute power over Homeworld and the existing Gem colonies.

Symbol
The symbol of the Great Diamond Authority appears on many Gem structures, and has changed over time. On structures built prior to the Rebellion, the symbol consists of four diamond shapes: White (top), Yellow (left), Blue (right), and Pink (bottom). On modern structures,as well as the partially-healed Centipeetle's drawings seen in Monster Reunion, the Pink symbol has been removed, leaving only the White, Yellow, and Blue shapes (now depicted in the form of overlapping triangles).

Yellow Diamond
One of the Diamond leaders. She is the superior of Jasper (As well as the former superior to Peridot), she is also the superior to countless other Gems made for her. She commenced the Cluster project when Earth was deemed unfit for a colony, due to the Rebellion. According to Peridot in "Hit the Diamond" Yellow Diamond is in complete control of the Gem Homeworld's military.

Subordinates

 * Peridot (formerly)
 * Jasper
 * Yellow Diamond's Pearl
 * Other Rubies

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

Subordinates

 * Sapphire (former court member)
 * Unknown court members
 * Ruby (formerly)
 * Other Rubies
 * Blue Diamond's Pearl

Unknown Diamond (White)
One of the Diamond leaders. Details about her are unknown, except for the fact that her white symbol appears alongside those representing Blue Diamond and Yellow Diamond on both ancient and modern Gem structures. Due to a naming pattern, her name is most likely White Diamond.

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

Pink Diamond
A Diamond leader. Details about her are unknown other than the fact that her pink symbol is present on the majority of ancient Gem structures, but absent on structures dating as early as the Pyramid Temple. She also has a mural in the moon base, but only her legs are present in the shot.

Pearl's space suit, as seen in "Space Race" and "Back to the Barn", has a pink symbol on its chest. This suggests that Pearl was previously involved with this Diamond. Sardonyx also sports pink diamonds on her feet, this most likely comes from Pearl.

Subordinates

 * Rose Quartz (formerly)
 * Jasper (formerly)

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 would never forsake the gem I was made for!". Gems who serve under the Diamonds will do anything to avenge their Diamond, as seen in Jasper's case in "Earthlings".

Trivia

 * The current symbol might be a reference to The Triforce from The Legend of Zelda, as they both are three triangles that form a symbol.
 * The former symbol resembles the NFPA diamond, with slightly different colors (one of the diamonds is red instead of pink) and with the colors' positions switched.
 * 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 episode "It Could've Been Great".
 * It is revealed in "Monster Reunion" that the Diamonds were the ones responsible for corrupting almost all remaining Gems on Earth.
 * Centipeetle only drew three diamonds when she was asked who caused the damage, so one of the diamonds wasn't involved with this weapon, presumably pink diamond, who is absent in symbols after the Rebellion.