|“||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.|
|“||How dare you fuse with a member of my court? You will be broken for this!||„|
|~ Blue Diamond to Ruby in "The Answer"|
Blue Diamond is one of the main antagonists of the Cartoon Network series Steven Universe alongside Yellow 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 is voiced by the Irish singer Lisa Hannigan.
Blue Diamond has a turquoise complexion. She has long light blue hair, plump lips, a straight nose, black eyebrows, and three eyemalashes each on the lower portion of her eyes, which are turquoise with diamond shaped pupils. Her gemstone is located on her chest and sometimes she is seen wearing a long, blue cloak, and a dark blue bodysuit with a cutout for her gemstone.
She is also noticeably tall in height like the other diamonds. This is clearly seen when her Blue Diamond's Pearl is standing next to her. Her mural portrayal from the Moon Base depicts her with either long dark hair or a long cloak.
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.
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.
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.
"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.
- Blue Diamond is the first of the Diamonds to be seen on-screen in an episode of Steven Universe.
- 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.