Yellow Diamond is the second-youngest member of The Diamond Authority, and the current commander of Homeworld's military practices. As a Diamond, she is one of the leaders of Homeworld itself and all of Gem kind.
As a Diamond, Yellow Diamond is naturally taller than most other Gems, towering over most with the exception of other Diamonds. She has a pointed, upturned nose, plump lips, and an unusually long neck. Her hair is a short bob with two spiked tips. She has black eyebrows, and black markings around both her eyes, which are bright yellow with diamond shaped pupils. She wears a dark yellow and olive bodysuit, as well as a short yellow tailcoat-like attire. She also wears yellow gloves and olive-yellow boots.
Yellow Diamond is a type of less sympathetic, and more critical authority figure when compared to the other Diamonds, possibly taking more of her personality pointers from White Diamond herself than Blue Diamond and Pink Diamond do. This is more evident through her debut, showing a similar cynical, all-knowing behavior White Diamond would show to her subjects, if not a little more assertive, most evidently shown during her interactions with Jasper and Peridot upon their return. She has shown to become easily angered at times.
Yellow Diamond isn't an exact copy of White however, and shown a more open mindedness towards subjects and events, recognizing that Steven Universe isn't Rose Quartz, and shouldn't be punished even after just being told that Pink Diamond had been killed by Rose. However, after Season 6 she might've lost all reason to idolize her.
Yellow Diamond is capable of producing, and efficiently using electricity as a weapon. Apparently the power of said electrical energy is connected to her emotion: the angrier she is the stronger the electricity.
Not too much is known about Yellow Diamond's background. Yellow Diamond is one of the first Gems created, White Diamond creating her and Blue Diamond to construct Homeworld, her being put in charge of the Homeworld military practices and placed as top commander.
Yellow Diamond makes her first official appearance in a messaging screen when Kyra contacted her, recognizing Kyra when she called her "Yellow Jacket". She brushed his threats off, believing an organic creature doesn't have much power compared to her, and when the duel was brought up, she claims she only didn't show up because she had better, more important things to do.
She appears on Homeworld when Jasper and Peridot made their return. Yellow immediately goes into questioning them, asking about their current state, and more particularly, the state of the Crystal Gems, and even more particularly, Kyra. When asked of Rupee, she simply answered and called her a test they're working with. When the duel between Jasper and Rupee, Yellow Diamond ended up being attacked by Kyra, getting her arm cut off in the assault. Soon after though, she called in Jasper and Peridot and banished them both from her city for the apparent false information they've given her.
When the Osicone appeared, Yellow Diamond ended up confronting the beast, but while she held up a good fight, she ended up poofed. She returns off-screen.
Yellow Diamond, after being recovered, spent her time working on the colonies, telling Blue Diamond how bored she was and wondering where all the excitement was when the Crystal Gems were around. She had Yellow Pearl go to Earth in order to give an updated report, as the other peridots were too busy.
She talked to Blue Diamond about this later on, but she was cut short when White Diamond herself came in to see her, apologizing for not preparing for her arrival earlier. She met with her outside alongside Blue Diamond, her informing her about the status of the inactive Rupee. She went with White Diamond onto the White Diamond Space Station and soon was informed about Sapphire's capture. Yellow remained quiet during the event, even after Blue Diamond got poofed by White for insubordination, but she did eventually tell her about the Crystal Gems and their victory in saving Homeworld, only to be told that it didn't cover their involvement in the Gem War. When the Crystal Gems and Mane Six were brought to the throne room, Yellow Diamond tried to convince her to stop, saying that she was unfortunately on their side in the argument, bringing up as well that they'll inform Pink Diamond once they find her. She then found out her true fate, but still said that Steven wasn't Rose, and therefore shouldn't be punished. When the fight broke out, she stood back and waited for it all to finish.
She has shown little involvement in this season. While she was distraught about the Pink Diamond reveal, she kept a level head about it and tried to comfort Blue Diamond over it. Her bigger involvement came when the trial happened, no longer having much compassion to the Gems, and insisting to have them executed straight away, and only getting irritated when she had to wait. She hoped for a stronger punishment than the banishment that they eventually got.
During a meeting with the Mane Six, Yellow then discovered Acid and Cyanide's involvement, and she forces them to reveal her location through electrical charges, and once she found out, instructed the Mane Six to get her, leaving the snakes with White Diamond.
She has shown little to no involvement up to the finale. While comforting Blue Diamond again, she was found by Connie Maheswaran, Sadie Miller, Lars Barriga, Onion's Gang, Jamie, and Connie II, and she was told about the capture of the Crystal Gems and Mane Six, and Yellow Diamond decides to offer them the Sun Incinerator to rescue them. Sometime later she was then informed alongside Blue Diamond about Chamber 77. Yellow states that they had a meeting to get to, and contacted White Diamond about it. She was told not to worry over it, but she decides to go to the chamber anyway, stating her arrival wasn't a request, and upon looking inside, only to find Pink Diamond within. She quickly confronted White Diamond shortly after this, putting all the pieces together and first confirming of her involvement on the matter as the killer. She calls White a traitor, before being captured and taken to be hybridized with Blue Diamond to create Green Diamond. She was broken out, and quickly attacks White Diamond, giving everyone else time to escape, and as they left to the Sun Incinerator, she and Blue Diamond split in order to rescue Pink Diamond from the Space Station.
During the first arc she was one of the Gems who went with White Diamond as part of her insisted vacation across the cosmos. She never truly agreed to the trip, and still shown a bit of resentment and suspicion towards her, especially since she took over the planet just prior to the event. During the trip she bonds with Bismuth over these issues. However, when they crash onto Orthix, she is hypnotized by White Diamond for a brief time before White realized she was flawed deeply and releases her.
Her role in the season is mostly minor, being put away from Homeworld thanks to Grogar, despite her anger in thinking no one believes she can protect herself anymore.
My Little Universe II
Near the end of the season, she appears with Blue diamond as she was called to the Spirit council by Teal Garnet, in defense for White Diamond and Discord. She also joins them in the final battle with Grogar's Army, staying behind in the Realm of Corners to give the Harmony Gems time to stop his fleets from leaving Homeworld. However, during the fight she and Blue got shattered by Grogar. She wasn't revived until after Grogar lost his powers, and Steven reviving them with his healing powers.