|“||How dare you fuse with a member of my court? You will be broken for this!||„|
|~ Blue Diamond to Ruby in "The Answer"|
|“||How curious. I'm impressed by humanity's ability to survive in the wild. What a strange planet, where else would a being as fragile as a human live? While a being as powerful as a Diamond, perish? This is where it happened. Where she was broken.||„|
|~ Blue Diamond to Greg.|
|“||I want to know what she thinks we're going to do with her. Because I want to do something worse.||„|
|~ Blue Diamond in the Steven Universe Wanted Promo.|
Blue Diamond is one of the main antagonists of the Cartoon Network series Steven Universe, along with Yellow Diamond and White Diamond. She is one of the Gem Matriarchs on Gem Homeworld and a member of the Great Diamond Authority ruling over Homeworld. She was apparently responsible for overseeing an attempted colonization of Earth, and later, the attempts to quell the rebellion of the Crystal Gems. She serves as the main antagonist of the Zoo arc in the show's fourth season.
She is voiced by Irish singer Lisa Hannigan.
Blue Diamond, as one of the rulers of Homeworld, is of a massive size, her height making a common Pearl pale in comparison. Her complexion is light blue, and her hair is a very pale shade of blue, appearing as off-white. Her hair comes together in the front to reveal her gem. She has a gaunt face, full lips, and a straight nose. She also possesses large, sad, slanting eyes, light blue irises, diamond-shaped pupils, thin, black eyebrows, and three black markings on the lower portion of her eyes resembling eyelashes. Her gemstone is located on her chest, and she wears a long, navy blue cloak. Underneath her cloak, she wears a navy blue cowl. She also appears to be slightly shorter than Yellow Diamond, who herself wears heeled boots.
Blue Diamond's debut portrays her as a very mellow Diamond who treats high-ranking members of her court with respect. According to Holly Blue Agate, Blue Diamond has a reputation for mercy and forgiveness. "Saving" Greg from the threat of the Cluster after taking a liking to him, unaware that the Cluster is no longer active, demonstrates this. However, as with Yellow Diamond, her true nature may be at odds with her reputation, as she sentences Ruby to shattering for accidentally fusing with Sapphire while trying to do her job and saving her by accident. However, it is unknown if her personality has changed over the millennia after Pink Diamonds death. Blue Diamond's temperament appears to have changed significantly in the 5,000 years following the death of Pink Diamond. She is currently in a state of great depression, still mourning over the shattering of her fellow diamond. She is unable to let go of the past, becoming fixated on preserving Pink Diamond's legacy. Her efforts to maintain the late diamond's zoo, save Earth specimens from the Cluster's emergence, and her refusal to shatter the rose quartzes that once served under Pink Diamond shows this behavior. She continues to regard the Earth as Pink Diamond's colony, and, due to being unaware that the Cluster is bubbled, is visibly saddened by the fact that the planet will eventually be destroyed. Additionally, Blue Diamond seems not to understand humans, given by how she was surprised that Greg was able to comprehend and sympathize with her pain of losing a loved one. Blue Diamond, as shown in the episode "The Trial", is extremely diplomatic. Against Yellow Diamond's wishes, she allowed Steven to continue making his case during his trial, though she did lose her temper when his recounting of events differed. She nonetheless seemed to want to hear Blue Zircon's theory on how and why Pink Diamond was shattered. When Yellow Diamond snaps and poofs both Zircons present at the trial, Blue Diamond confronts her and scolds her for not having enough restraint to hear the case out. This shows that Blue Diamond may be as merciful and forgiving as her gems claim – at the very least, she certainly has a greater respect for due process and an interest in the truth.
- Radiated Pathokinesis: When Blue Diamond is overwhelmed with sadness, she emits a blue aura around her that induces the said emotion to anyone exposed to it. The induction is powerful enough to cause Gems exposed to the aura to cry immediately unprovoked. The ability does not seem to affect non-Gem beings, as Greg and Lars were not affected by it. It also affects Steven since he is a half-Gem. It's unknown if this is limited to sadness or if she can do something similar with other emotions.
Blue Diamond is one of the members of the Great Diamond Authority alongside Yellow Diamond, Pink Diamond and, presumably, White Diamond (possibly sisters). As the matriarchs of Gem Homeworld, she was in charge of colonizing planets for Gem colonizations and expansion.
In "The Answer" Blue Diamond appears on-screen for the first time in a Garnet's story narrating how Ruby and Sapphire met each other. It is revealed that she was once the supervisor of the colonization of Earth following the death of Pink Diamond at Rose Quartz's hands. To make sure the progress of colonization was completed, she had a Sapphire predicting the further events to come. However, when Ruby risked her life to save Sapphire's they fused into Garnet and gave enough time for Rose Quartz and Pearl to escape from the battle arena. When this happened, Blue Diamond angrily threatened Ruby that she would be shattered for fusing with one of her court members and for letting the rebels escape. However, Sapphire took Ruby from the hand and left the arena falling to the earth surface in time. Blue Diamond was never seen again through the episode after that. In "It Could've Been Great", Blue Diamond's mural is seen on the moon base alongside Yellow, White and Pink Diamonds' and is mentioned by Peridot too.
In "Back to the Moon", Blue Diamond's mural is once again seen on the moon base when the Crystal Gems and the Ruby Squad went to visit the place.
Blue Diamond appears in "Steven's Dream" in her first onscreen appearance, Blue Diamond returns to Earth one last time to pay her respects to Pink Diamond before, as she believes, the Cluster will emerge, unaware that Steven had contained the superweapon months earlier. Blue Diamond expresses regret over how she should have done more, and wonders what Pink Diamond would think of the Cluster destroying her colony. After Greg reveals himself, Blue Diamond asks her Pearl to bring Greg to her. She then states how she is impressed by humanity's ability to survive in the wild and remarks on the irony that a fragile human can survive on Earth while a being as powerful as a Diamond can perish. When Greg tells her that he also lost someone close to him, Blue Diamond is surprised that a human can sympathize with her, and is glad that she can save Greg from the Cluster. She forcefully takes Greg and boards her ship with the goal of bringing him to Pink Diamond's Zoo.
In "Gem Heist" Holly Blue Agate reveals that after Pink Diamond was shattered, Blue Diamond took over her Zoo in an attempt to preserve her legacy. Blue Diamond and Holly Blue have been maintaining the Zoo since Era 2 began.
In "That Will Be All" Blue Diamond returns to the Zoo to mourn alongside a room full of bubbled Rose Quartzes. She is shocked to find Yellow Diamond entering the room, and tells her that she just wants to cry alone. Blue Diamond listens to Yellow Diamond's song, comforts Yellow when it ends, and is greeted afterward by Holly Blue Agate and the Crystal Gems. Blue Diamond does not understand what Holly Blue means by Sapphire's "special delivery". Once Sapphire lies, and tells her that she foresaw Blue Diamond requesting more humans for the zoo, Blue Diamond believes her, and is sad to announce that there is limited time to retrieve more humans due to the Cluster.
In "The Trial", Blue and Yellow Diamond attend the trial of "Rose Quartz" (Steven) after he is brought to Homeworld by Aquamarine and Topaz. After arriving at the trial, Yellow Diamond states that they should shatter Rose Quartz just for how ugly her new form is, however, Blue Diamond states that she wants to hear Rose's case and wants to know what she thinks they will do to her, because she wants to do something worse. After Ruby comes in as a witness and does massive damage to Rose's case, Blue Diamond, unlike Yellow Diamond, opts to hear out the defense anyway. After Steven confesses to shattering Pink Diamond, Blue Diamond demands to know how, and when Steven doesn't recall exactly how it happened, Blue shouts at him, telling him that Rose used a sword (also using her Pathokinesis to make everyone in the room cry). After the recess break, Blue Zincron, upon having the sudden realization that Pink Diamond being shattered by Rose Quartz doesn't make sense, presents Blue Diamond's Palanquin to the Diamonds and asks where Pink Diamond's Pearl, Sapphires and other gems were to protect her or predict Rose's arrival, coming to the conclusion that another Diamond was the only gem that could have gotten anywhere close to Pink Diamond without anyone being alarmed, although her and Yellow Zicron's forms are destroyed by Yellow Diamond immediately afterwards. Blue and Yellow Diamond then get into an argument over the point of investigating Pink Diamond's death, leaving Steven and Lars to escape using the Palanquin.
- Blue Diamond is the first of the Diamonds to be seen on-screen in an episode of Steven Universe.
- However, Blue Diamond was not the first of the Diamonds to be revealed in Steven Universe media as a whole. The extended theme song reveals Yellow Diamond.
- Blue Diamond's appearance and her throne appear to be heavily influenced by Indian Muslim culture. Her clothing resembles that of traditional Arab wedding dress, specifically a Henna dress. The frame of her throne has carved geometrical designs for windows, which are a common design in many Indian temples and houses.
- The largest blue diamond, the Hope Diamond, also originates from India.
- She somewhat bears resemblance with Connie's mother.
- Her appearance in "The Answer" is similar to Emperor Palpatine from Star Wars.
- Despite being a Diamond like Yellow Diamond, the cut of her gem does not exactly match her yellow counterpart, in contrast to other gems of the same type, who appear to share color and cut. However, since the two episodes they appear in were storyboarded by different members of the crew, their gemstones may only look different due to the differing art styles of the crew members, as they appear to be of the same design – a rhombus-shaped decahedron with a rhombus facet and four rectangular facets on the sides.
- When she appears for the second time in "Steven's Dream", Blue Diamond's gemstone now bears a closer resemblance to Yellow Diamond's.
- Blue Diamond's importance is further emphasized, as she has her own palanquin with a curtain in the front and spider legs to move it around on its own.
- Rebecca Sugar has mentioned that blue colored Gems are mainly diplomats.
- Rebecca stated that Blue Diamond's character design is meant to look "ghostly" to get the feeling of her mourning, and draws much influence from Martha Graham's Lamentation ballet dance. Her face and hair designs are also inspired by Leiji Matsumoto's art, to make her come across as a "strange presence."
- Much like Ruby and Sapphire before "Hit the Diamond", all Blue Diamond and Yellow Diamond's main appearances have been in episodes featured in a StevenBomb.
- According to her mural, Blue Diamond ruled nine planets during the attempt to colonize Earth.
- Since it has been thousands of years since then it is possible she rules over more planets now.