This article contains information that is considered canon in the "Steven Universe" universe.
That's what you think! I am an eternal flame, baby!
Ruby has bright-scarlet skin, dark red eyes and dark burgundy hair. She is slightly taller than Steven. She wears a maroon tank top and a matching colored headband around her thick and fluffy, outgrown hair cropped at the neck. Her ensemble includes mid-thigh burgundy shorts, and short, pointed maroon boots similar to Amethyst's. Her gem is located in the palm of her left hand and has a square facet.
Approximately 5,750 years ago, Ruby lived on Homeworld as a common foot soldier.
Homeworld was attempting to create a new colony on Earth, which was overseen by Blue Diamond. She was part of the diplomatic team sent to stop Rose's Rebellion on Earth, as one of the three Rubies assigned to guard Sapphire, a gem with prophetic vision, who was valuable for the dismantling of the rebels. When these attacked, the three Rubies fought back, attempting to fulfill their jobs, only for two of them to be poofed by Rose Quartz and Pearl before targeting Sapphire.
Before her imminent poofing, Sapphire thanked Ruby for her service, at which point Ruby realized Sapphire had already predicted this and that she knew she would be destroyed. Unable to accept that she had failed her mission, Ruby tackled Sapphire to protect her from Pearl and caused them to accidentally form Garnet, the first fusion between Gems who were not of the same kind, changing the prophecy foretold by Sapphire. They immediately defused and were surrounded by an angry crowd. Furious that Ruby interfered with the outcome of the battle (and participating in an unsanctioned fusion with a member of her court), Blue Diamond ordered that she be shattered. However, Sapphire grabbed Ruby and jumped out of the Cloud Arena towards the Earth below, landing them softly with her levitation.
Ruby was distraught that she was unable to protect Sapphire. When it began to rain, she carried Sapphire to a cave for shelter, where she saw Sapphire's single eye for the first time. The two talked about their experience and feelings being fused as Garnet.
Ruby and Sapphire grew closer and eventually decided to fuse again. Garnet was found by Pearl and Rose shortly after forming. Upon being met with acceptance and not revulsion, she began to bombard Rose with questions about the events and circumstances that allowed her to become Garnet, as well as her own feelings about existing as a fusion. Rose told her to "never question this", and said that she was already the answer to all her questions--love. This would be the beginning of Ruby's existence as part of Garnet for the next few millenia, fighting Homeworld with the Crystal Gems to protect Earth.
Ruby can't avoid the inevitable. She's just letting her emotions get out of hand.
|—Sapphire, "Keystone Motel"|
According to Rebecca Sugar, Ruby "has no sense of what’s going on around her" and "can only focus on one thing only at the expense of all things". 
Ruby mainly embodies Garnet's strength and courage, while Sapphire embodies Garnet's cool nature and calm under pressure. Ruby is extremely passionate and emotional. She is known to have a short temper and violent ways of exhibiting her anger; this is best seen in "Keystone Motel", when she was infuriated to the point of using her thermokinesis and boiled the motel pool, even summoning her weapon at The Best Diner in the World. Ruby is also very willing to admit when she has taken her anger too far and will admit when she is in the wrong. She seems to put the welfare of Sapphire above all else, doing everything to find her, and immediately made sure that Sapphire was well. When Garnet is extremely disturbed, Ruby also appears to show the most visible reaction in comparison to Sapphire. This is best demonstrated in "Keeping it Together", when Garnet's left eye began crying. After poofing the big Cluster prototype, Ruby and Sapphire started conversing with each other through their respective sides of Garnet, Ruby arguing that the forced fusion experiments were Homeworld's retaliation against the Crystal Gems for their rebellion. Although Sapphire did not express much emotion towards the situation, Ruby was clearly angered at the revelation of Homeworld's experiments and became hysterical.
When not angry, Ruby is a suave romantic, soft with words, and quite flirtatious towards Sapphire. When she channels her emotion on love rather than on rage, she can be affectionate and extremely caring, feeling the need to protect, and even cool down for, those who she truly loves. These moments of calm also bring out the playful tease inside her, which is, for the most part, trapped under her wild emotions. Ruby also places much value in trust and fusion, being absolutely outraged with Pearl when she learned she was tricked into fusing into Sardonyx. She appears to be a bad conversationalist, occasionally speaking in somewhat unintelligible mumbles, a trait which she carries onto Garnet.In "The Answer" it was shown that Ruby originally had very little sense of self-preservation or individuality, willing to take the blame for fusing with Sapphire and was content with her own inevitable destruction, arguing that there are "tons of her" in reference to the various identical Rubies found on Homeworld. She still possess this to an extant as seen in "Jail Break" when she was only worried about Sapphire and said "Who cares?" when Sapphire asked if she was hurt.
Like all other Gems, Ruby can change shape, invoke a weapon, and take refuge in her gem to heal. Ruby seems to possess greater strength than most Gems, as she was able to shake the walls of her prison with a single punch, lift Sapphire with little effort in "Jail Break", and flip a diner booth table with relative ease in "Keystone Motel". Like all Gems, Ruby can fuse with other Gems.
- Ruby can fuse with Sapphire to become Garnet.
- Garnet can fuse with Amethyst and become Sugilite
- Garnet can fuse with Pearl and Amethyst and become Alexandrite
- Garnet can fuse with Pearl and become Sardonyx.
- When fused with other rubies, they form a larger Ruby.
- Gauntlet Proficiency: Through sheer anger and feeling the need to release it through violence, Ruby can summon a gauntlet like Garnet's. Although only seen once, it is clear that Ruby possesses some knowledge of how to use it.
- Thermokinesis: Ruby has the ability to increase the temperature and generate heat. This is shown in "Keystone Motel", when her body gets so hot that it begins burning the carpet of the motel room, and when she boils the pool to nothing but steam in a very short amount of time. It is shown to be relate to Ruby's emotional state. As the ability manifested itself when she got furious in the aforementioned episode and when she felt infatuated in "The Answer" as she set the grass beneath her ablaze when Sapphire thanked her.
- Heat Resistance: Ruby has not demonstrated this ability, but it was confirmed that the only reason Garnet can swim in lava is by Ruby.
I don't think you're stupid!
|—Sapphire, "Keystone Motel"|
She and Sapphire have a romantic relationship, shown in "Jail Break", when she immediately panics when realizing that the two have been separated and becomes reckless trying to find her, trying to pass through the energy field (as hinted by the screams of pain heard at the beginning), running around without checking if Peridot and Jasper are around and loudly shouting for Sapphire whenever she stops singing. When she finds Sapphire, the two embrace and Sapphire kisses away Ruby's tears, showing their romantic relationship. Ruby cares strongly for Sapphire's well-being, as she expressed deep concern for possible injury. Garnet's dialogue in "Love Letters" implies that Ruby and Sapphire's relationship developed gradually over a period of time. "Keystone Motel" reveals that their relationship can be strained at times due to Sapphire's precognition, causing her to be preoccupied with the outcome of events, instead of the events as they happen. This puts her at odds with the passionate Ruby, who very much lives "in the moment". In this episode, Ruby was furious over Pearl's deception in "Cry for Help", but Sapphire wasn't because she had seen that in the future they would all get along again. This greatly irritated Ruby, as she felt that Sapphire was acting cold, uncaring, emotionless and distant. By the end of the episode, she sees how much the ordeal actually affected Sapphire and, realizing that being furious was helping nobody, apologized for her behaviour.
But I think they'd work it out if they'd just talk to each other!
|—Steven, "Keystone Motel"|
At first, Ruby seemed distant towards Steven, only focusing on finding and forming Garnet with Sapphire as soon as possible. In reality, Ruby cares deeply for Steven, as hinted when she tries to tell him not to put his hand through the force field for his own safety. Garnet also says that both her and Sapphire had already loved Steven when he asked if he made a good first impression. She was also upset by the fact that their plan of revealing themselves on Steven's birthday had failed, apparent when she said to Steven, "Oh, great! This is just perfect!" and "Don't look at me!" In "Keystone Motel", she obliges in Steven's attempts to calm her down, and upon seeing how Steven was affected by her and Sapphire fighting, Ruby and Sapphire both felt very guilty and made up.
You met Ruby and Sapphire?!
|—Amethyst, "Jail Break"|
Pearl and Amethyst have been aware of Garnet's true identities for several millennia. Their perception of the two while separated remains unknown, but given their good relationship with Garnet, it can be assumed it is a positive one. Ruby holds a great deal of trust and respect for their teammates and becomes furious when Pearl betrays that trust in "Cry for Help".
This is punishment for the rebellion!
|—Garnet, "Keeping it Together"|
I don't feel like forgiving Pearl!
|—Garnet, "Keystone Motel"|
Not much is known about the relationship between Ruby and Pearl, except during "Keystone Motel", where Ruby feels used after Pearl tricked Garnet to fuse with her by rebuilding the Communication Hub twice. Ruby was very angered by this, which contrasted Sapphire's opinion of wanting to forgive Pearl, even leading to them unfusing.
Oh, boy... Where's the other one?
|—Greg, "Keystone Motel"|
Not much is known about her relationship with Greg, but Greg at least knew that she and Sapphire were the fusion components of Garnet, and considering most humans aren't close enough to her to know this knowledge, this at least shows he knows her rather well.
Not much is known of Ruby's specific opinion on Lapis Lazuli, however, if it is anything like Garnet's, she is rather indifferent about her and would possibly look at her as not much of an ally, but not much of an opponent either. Upon meeting her in "Jail Break", she says, "Oh, it's just you...", implying that she holds more of a negative attitude towards Lapis Lazuli.
- "Fusion Cuisine" (cameo)
- "Jail Break"
- "Love Letters" (mentioned)
- "Keeping it Together" (mentioned)
- "Keystone Motel"
- "Friend Ship" (mentioned)
- "Too Far" (mentioned)
- "The Answer" (flashback)
- We are the Crystal Gems (non-speaking)
- What Are Gems? (gem only)
- Fusion (non-speaking)
- Although she was not formally introduced until "Jail Break", her first appearance was in "Fusion Cuisine".
- When Alexandrite is separated, her silhouette, along with Sapphire's, is noticed. To the left of "Garnet" is seen as Ruby, and to the right of "Garnet" is seen as Sapphire.
- Garnet and the other Crystal Gems had planned to wait for Steven's birthday to introduce Ruby and Sapphire to him.
- When asked if Ruby was blind, Joe Johnston merely stated that she was "used to being fused with Sapphire, and so, used to having two types of vision", making the theory of Ruby's blindness not at all likely. 
- Ruby possibly has her own room in the Crystal Temple, as the Temple Gate has a red gem and a blue gem that Garnet opens simultaneously.
- Most of Garnet's sensitive side seems to come from Ruby; whenever Garnet cries, her tears fall from her right eye (the red-colored one) that represents Ruby.
- Ruby cried when she and Sapphire met again in "Jail Break", while Sapphire herself appeared to remain calm in "Keeping it Together" after meeting the Cluster Gems.
- Ruby is the birthstone of Rebecca Sugar.
- During times of great conflict of opinion, she and Sapphire are able to talk to each other individually through Garnet, as shown in "Keeping it Together" and "Keystone Motel".
- In "We are the Crystal Gems", Ruby is shown to be cracking or holding her knuckles, a sign of toughness, or that she's ready to fight, while Sapphire is holding her hands together, interlocking her fingers.
- This shows that she is calm, graceful and passionate. On the other hand, Ruby seems calmer than expected from her, and Sapphire more upbeat than usual, possibly indicating that being Garnet brings balance to their personalities.
- Ruby is denser than water, and, as such, she sinks in the pool in "Keystone Motel".
- Ruby's thermoregulation of raising the temperature directly opposes Sapphire's thermoregulation of lowering the temperature, representing their polar opposite personalities.
- Ruby's ability to raise the temperature is somewhat of a pun, being that in "Keystone Motel", where Ruby is quite literally letting off steam, and acting like a "hothead". This is also shown when Sapphire says, "She'll eventually just burn herself out."
- Ruby and Sapphire's relationship is quite the literal riff of the phrase, "fire and ice."
- Garnet's electrical manipulation stems from Ruby and Sapphire's combined abilities, as thunderstorms can result from the formation of masses of cold and warm air.
- Although Ruby's gem is in her left palm, she is shown summoning her gauntlet on her right hand.
- Ruby's gem cut is a square, while Sapphire's is a triangle. While triangles are self-sustaining in that each side of a triangle supports the other two, squares are not (i.e. a freeformed square can be changed into a rhombus without stretching or contracting sides). This could be a metaphor for Ruby being the hotheaded counterpart to Sapphire, as she is shown to "collapse" easily as well.
- Ruby's short temper combined with her stature is a reference to the "Napoléon Complex" stereotype.
- According to Garnet in "The Answer", Ruby and Sapphire met 5,750 years ago.
- Currently, all of Ruby's physical appearances and major roles have occured in episodes featured in a StevenBomb.
- Rubies are composed of a material known as corundum, the second hardest crystal structure after diamond (9,10 on the Mohs Scale of Hardness).
- Since ruby is a member of the corundum group, it is closely related to sapphire and thus shares some properties with it, such as hardness, composition and double refraction.
- In its pure form, corundum is colorless.
- Rubies are the most expensive colored stone, going by carat.
- The word “ruby” comes from the Latin ‘ruber’ meaning red and, like many other gemstones, the ruby’s symbolic meaning is heavily dependent on its coloring.
- Natural ruby is one of four “precious” gemstones (including diamond, emerald and sapphire), known for its rarity, monetary value, and hardness (second only to diamond).
- Natural ruby can be distinguished from synthetic ruby by its inclusions; natural ruby typically exhibits inclusions, whereas synthetic ruby tends to be eye clean.
- The color of ruby is its most important quality factor. The most sought after color is a strong pure red to red with a hint of blue, called pigeon's blood.
- The vivid red color of ruby means that it is associated with desire, and it is thought by some to be a stone of love with an aphrodisiac effect.
- When the color of ruby is too light, it is classified as pink sapphire, but the line between pinkish-red ruby and pink sapphire varies by region.
- The ruby is closely associated with aspects such as vitality, life, passion and fire, all of which can be symbolically linked to the color red.
- This shows in Ruby's emotional temperaments and overall emotional/angry attitude as well as her strength.
- It is said that rubies can over-stimulate people who are sensitive or irritable.
- Ruby is the traditional birthstone of those born in July and is also the zodiacal stone for Cancer and Aries.
- Ruby is also used to celebrate the fifteenth and fortieth wedding anniversaries.
- The day assigned to ruby is Tuesday (hence the Rolling Stones song, "Ruby Tuesday").
- The planet Mars is famously known as “the red planet”, due to the high concentration of iron oxide (basically rust) on its surface and rubies, along with all of the aspects mentioned above, have been linked with Mars in one form or another.
- Ruby is the national gemstone of Burma and Thailand.
|Ruby has a red stone in her left palm. It has a square aspect, the front and back are symmetrical, and it has a light pink ring around it, which is usually hidden inside her body, except when she is regenerating. It is a decahedron, specifically a truncated tetragonal dipyramid.|