The Great Galaxy Authority

The Great Galaxy Authority is a matriarchal body of Gemleaders consisting of Red Diamond, Purple Diamond, Chrome Diamond, Orange Diamond, Brown Diamond, Eliza Anderson, and formerly Green Diamond, Silver Diamond, and Black Diamond. They are the absolute ruling power over their Homeworld and any of its remaining colonies still in existence.

Overview
The Great Galaxy Authority has complete control over every gem made on their colonies. Each Diamond rules a certain aspect of gem society. Gems made for the Authority are split into groups, frequently known as Courts, among each Diamond. Some belong to Chrome, Others Purple, more to Red, etc. Gems usually have a diamond with the color corresponding to the Diamond they serve.

In order to expand their reign, The Great Galaxy Authority colonizes planet. Each Diamond owns a certain amount of colonies and are in charge of and making sure the planets are used to their fullest potential for Gem-Production. The Galaxy Diamonds have their own hierarchy outside of their strict Caste System, with Black Diamond formerly being at the bottom, which was replaced with Eliza Anderson. Red Diamond appears to take the top of this hierarchy due to her originating the whole group.

Displays of Loyalty
Most gems are very loyal to their Diamonds and openly express it, with most being fanatical about their Diamonds, believing their the most elite beings to ever exist in the universe. The loyalty is so much so that multiple Gems have tried to "avenge" the late Black Diamond, since she was their Diamond.

Expected and Appropriate Behaviors
Gems must show respect to their Diamond Leaders. An expected behavior is calling a Diamond "My Diamond" and form the shape of a Diamond on their chest using their arms, and optionally giving them many gracious titles before speaking to them, mostly starting out with their main title (The Ominous Red, The Mighty Purple, The Radiant Chrome, The Loveable Orange, The Generous Brown, and The Bubbly Green/Eliza).

Symbols and Logos
The Logo of The Great Galaxy Authority appears on most- if not every -gem structure. On structures on the ancient parts of their Homeworld you can see a logo that had a Large Red Diamond with a small Green Diamond in the middle. On not-so-much more ancient buildings you can see a logo with a Red Diamond, Purple Diamond, Grey Diamond, and Orange Diamond. You can also find the Galaxy Star Logo on newer buildings and scarcely you can find the newest logo on buildings- with most being remodeled to fit the new logo.

History
The exact history of the Diamonds themselves is unknown, including mostly when and how they themselves came to be. Based on the murals in their Moon Base, Red Diamond was created first, followed by Green, Then Silver, then Purple Joined, then Chrome emerged, Then Orange, then Browns Arrival and finally Black. What is known, however, is that the Diamonds were to be eternally considered the most perfect, powerful and absolutely flawless Gems by virtually all of their peers, and it can be assumed this is how they rose to power over the entirety of the Gem species, using the influence they gathered to collectively cull a massive following of any "lesser" Gems. When the Great Diamond Authority was officially formed, the Diamonds developed and established several laws and rules to govern and essentially shape Gem society to their own designs, an influence that has lasted for untold eons all the way to the present.

At some point, the Diamonds imposed a social hierarchy on Gem society based on an individual Gem's abilities and skills and how they would best serve the Diamonds' goals. Those deemed better and more useful received different privileges than others; this created pockets of both inferiority and superiority complexes due to inequalities and the established knowledge of numerous Gems ranking lower while fewer Gems ranked higher (in many cases). In order to keep the system intact, "fusions" between two or more different types of Gems was and is still not allowed for low class members. This prevented two or more lower-class Gems from fusing and altogether becoming a different Gem, usually one considered higher up in the system. In addition, the Diamonds divided Gems into groups that appeared to partially be based on color; some belonged to Red, some belonged to Purple, etc. All Gems were usually required to wear uniforms with a Diamond insignia to signify the Diamond they belonged to.

The Diamonds also appeared to be in charge of different aspects of Homeworld and as such divided Gems accordingly into different groups for the purpose of carrying out any related duties; Purple Diamond was said to be in charge of Homeworld's military and Chrome Diamond/Eliza Anderson was stated to have control over Homeworld's diplomacy.

According to "The Expansion", the Diamonds wished to spread their "perfection" throughout the universe and expand the Gem race into a greater almighty empire. To do this, the Diamonds  turned the Gem species into a spacefaring race, expanding outward from Homeworld to colonize other places beyond their home galaxy. Upon colonizing a suitable planet, over an indeterminate period of time, the planet's resources were used to create new Gems, installations, structures, and outposts. Worlds colonized ranged from proper planets and moons to mere asteroids. Planets possessing a biosphere of any sort were not avoided and habitable planets might have been preferred as potential colonies over barren, lifeless worlds due to the rich organic minerals commonly found there. As stated time and again before and first shown in some recent roleplays, the completion of colonization efforts on a habitable world would inevitably lead to the extinction of all life existing on said planet and render it inhospitable to non-Gem lifeforms. Based off Homeworld's overall indifference, if not ranging from slight disgust to outright contempt towards organic life, it appears there were no qualms over colonizing worlds that had native life and what the completion of said colonization would mean for them in the long run. It is unknown how many of the Diamonds' current and previous colonies once possessed a biosphere before the completion of their colonization. Once a colony was completed, it was firmly established when Gems were created on a certain Diamond's planet they belonged to them by default. For example, Gems made on a Red Diamond colony belonged to her.

Red Diamond
Red Diamond is the leader of the whole Authority. She is thus the paramount ruler of all Gems and the intergalactic Gem Empire. She is very stern and insincere compared to her other Diamonds, who let most emotions control their life.

She made her debut in The Great Galaxy Authority Animatics | Orange Diamonds Emergence.

Purple Diamond
Purple Diamond is the right hand-man of Red Diamond. Not much is known about Purple except for the fact his Mural appears in the many Moonbases across their empire and a representation of him on every logo after Green Diamond.

He has yet to make a debut, but he was pictured in Galaxy Diamonds' Furiousity | Black Diamonds Shattering.

Chrome Diamond
Chrome Diamond is the lead of Aristocrats on the Authority. He is very strict but has yet to shattering or punish a gem during a RP or Video. He appears on the logo and has conquered 10 planets

He has also yet to debut but he was pictured in the same video as Purple Diamond.

Orange Diamond
Orange Diamond does not have a defined control of anything but she is leaning toward the production of Gems' and scouting Planets out to colonize. She appears on the logo and has control of 6 planets in total.

She debuts in the animatic Red appears in.

Brown Diamond
Brown Diamond is the lead on the schematics of Gem Buildings and their resources. His personality has drastically changed from a mourner to an easy going colonizer, much like Blue Diamond when Pink turned out to be truly alive. He appears on the logo and have multiple colonies under his belt.

He is pictured in "Call to Brown Diamond" and has made a debut in the Animatic "Split Family" by YouTube User IceDiamond.

Eliza Anderson
Eliza is the Daughter of former Member Green Diamond. She has not assumed any duties of her mother as of current. She takes the place at the bottom of the logo. She is the first Human-Hybrid Diamond on the Authority and likely the last/only.

She has not debuted or has been mentioned in any video, very much like her mother.

Green Diamond
Green Diamond is the first Diamond Red grew. She faked her own shattering for freedom on her Colony Earth, much like Rose Quartz did. She gave birth to a child in the form of Eliza Anderson. After this, not much is known about Green Diamond.

Black Diamond
Black Diamond was a former Diamond accidentally made by Red. She emerged during a Roblox Roleplay. Ser colony Earth, a rebellion outbroke and it ended with Blacks shattering. Black's death affected everyone except for Red and Purple Diamond.

Trivia

 * All of the Diamonds have diamond-shaped (rather than circular) pupils.
 * The confirmed instrument of the Diamonds is a synthetic sound combining harmonette and strings, processed by a synth, this can also be heard in "Same Old World" and "Monster Reunion" when the Corrupting Light flashes. It was revealed in the Steven Universe: Art & Origins book that each Diamond also has a unique chord.