Pink Diamond is a defective Gem member of The Diamond Authority, and the once initial ruler of Earth during its time as a starting Gem colony. She is also the youngest of the Diamonds. However, she was believed to have been isolated and "killed" by White Diamond, which triggered the Gem War, when in reality she took the form of Rose Quartz to protect the planet and remove herself of the role as a Diamond. She is the mother to Steven Universe.
Pink Diamond wore a magenta-pink and dark magenta top, which was cropped in the middle to reveal her midriff and gem, with large, puffy pink and white shoulder pads, magenta pink gloves, and a small pink and white skirt. She also wore magenta pink pants which were short and puffy, white stockings, and a pair of pink slippers with white pom poms floating over each of them.
She had rose pink skin, short, large, fluffy pale pink hair, and magenta eyes with diamond-shaped pupils. Pink Diamond, like Rose, appeared to wear lipstick. Her pink gemstone is located on her navel and displayed in a large pentagon-shaped opening.
A difference between her and the other Diamonds is that her gemstone is an inverted-side view of a round-cut diamond as well as being smaller than her peers. Nonetheless, she is still much taller than lower-ranking Gems.
As evident in Dream A Dream, according to Steven Universe's dream, Pink Diamond is (or was) a child-like individual, showing a lot of excitement and assertiveness, making sure her feelings are well known and heard loud and clear. As a young Gem, she is shown a spoiled sort of behavior, throwing into a tantrum when Yellow Diamond kept pushing her away from trying some of the Gem tech at the time. Despite this, she is also shown to be more sympathetic towards numerous Gems, mostly evident in her interactions with Pearl.
However, being on Earth significantly changed her outlook and demeanor, learning to love life and desiring to be free of Gem society. This led to her decision to abandon her life as a Diamond and become a rebel in the form of a Rose Quartz.
Pink Diamond was the youngest (and smallest) member of The Diamond Authority. Evident in Steven's dream, Pink Diamond was brought onto the Jungle Moon under Yellow Diamond's supervision. The main interaction we get to see was an argument between the two, Pink demanding a colony of her own, and claiming she was just as important as the rest of the Diamonds. Sometime after this, she was eventually given the option to choose her first Pearl, though found it difficult as all the pearls looked the same. She at first wanted to receive all the Pearls, which she was quickly denied of, and then pointed out Pearl from the crowd. She brought her back, and got to understand what Pearls were truly about and how little freedom a Pearl actually had, leaving her appalled that there was Gem not allowed to even leave their home. She was then confronted by her new advisor, Orchid, informing her she had received her very first colony: Earth.
On her arrival, she immediately started to enjoy her planet for it being so vibrant and different from other colonies, deciding to make the Prime Kindergarten right next to a apple tree she found, as she found it as a gift since it had pink flowers blooming at the time. Overtime, she began to explore her planet, discovering the concepts of dynamic change after observing the growth process of butterflies. Inspired, she insisted that Pearl try it, and to "surprise her" on what form to take. On seeing her, Pink Diamond was very pleased. One day, she discovered her tree "shattered", learning later on that it was just the process of a colony. This got her to convince the other Diamonds into making the Human Zoo to salvage some of the life, under the idea it to better study them. Later, during one of their trips, she and Pearl end up fusing together to form Rainbow Quartz. They separated after a short dance, Pink Diamond deeply enjoying it and deciding to keep it as their little secret after being warned by Orchid of what could possibly happen if they would say this to anyone.
She was later informed by White Diamond herself to come to Homeworld in order to deal with a "Situation". She arrived, and when seeing Kyra, at first asked if she could keep him in the zoo. After the fight however, remembering what Kyra had said, she realized how wrong she was to put humans in the zoo, and was given two options by Orchid: to convince them to stop, or to remove herself altogether. She at first attempted to convince the Diamonds that the colony was in threat of Rose Quartz and the Crystal Gems, but didn't work, the others tired of her excuses. Pink Diamond finally admitted her love for her planet to them, and that she should decide what to do with her own colony, just to be isolated by White Diamond, and basically told that she didn't have the freedom and the colony would be finished "with or without her".
After a long discussion, she, Pearl, and Orchid decide to put up a stage to set up her shattering. Before they could even start, White Diamond found her, and planned to kill her altogether much to her surprise, White claiming that she was an Off-Color, and that she never said that she was going to go home in order to take the planet from her. Pearl (as Rose Quartz), went out to finish the plan, but Pink Diamond was skewered, her gemstone narrowly being missed. After reforming, she took identity as Rose Quartz.
Much of her abilities could be seen throughout Rose Quartz, and by extension Steven Universe, the most notable being the Gem shield weapon all three shared.