Bismuth is an original Crystal Gem from the Gem War, and who've been in charge of making the weapons needed for the entirity of the team during the days of Rose Quartz. She wouldn't reappear again until she was released from the bubble inside Lion's mane. how she ended up there exactly is unclear.
Bismuth is the largest member of the Crystal Gems, about Jasper's height, but larger in width and possibly more muscular. Her skin is shown a dull blue, with a star "tattoo" on her shoulder as her symbol of a Crystal Gem. Her hair is braided, and has multiple colors much like her gemstone: yellow, green, pink, blue, violet, and dull orange. Unlike any other gem presented in the story, her Gemstone is interior, and caves into her body, while any other Gemstone presented is shown outward onto the body.
Her outfit is reminiscent of a medieval blacksmith, colored in a dull red and pink. She has a starlike symbol that goes around her apron.
Bismuth is mainly shown as very enthusiastic and is very passionate about her status as a Crystal Gem. Being a big voice of the Gems, she is shown on numerous ocassions as giving confidence, support, and encouragement to other Gems, namely on her side. While she is a very supportive Gem, this is only evident to Gems on her own team, as those on the opposing side get little to no sympathy from her, and someone she'd rather shatter than befriend if she could help it.
Her views on good and bad are a bit more black and white when compared to the other Crystal Gems, and she will quickly turn on one of her own team members if something prompts her to, most notably when she turned in Peridot after accusing her of being a spy for Homeworld, and turning on her again after the fact when she found she never told them of The Cluster. She seemed to become a bit more open though as the series progressed, as in The Sound of Silence, she tries to protect Pearl from Flint's accusations despite their suspicions over her involvement with the Pink Diamond case, yet doesn't try to hurt Flint when she found Pearl poofing herself over the situation, believing it was White Diamond's fault instead of his.
It is revealed in My Little Universe II that she has a respect for history, namely shown involving the history behind the Strawberry Battlefield and all of the stories behind all the weapons present there.
It is unclear as to Bismuth's origin, but at one time, she did go with a number of other Gems when they stumbled upon Equus a long time ago, instructed by Yellow Diamond to study it. She went to various areas, including Yakyakistan, Griffonstone, and Neippon, and in the end, she was simply told to leave, Bismuth believing that Yellow was too weirded out by the planet.
She then went to Earth sometime after, and began to build various Gem locations upon it when she was convinced to rebel by Rose Quartz, who got her to "open her eyes", and be who she wanted to be. She decided to become a blacksmith for the Crystal Gem army, and during her involvement she convinced Fulgurite to rebel, and during one fight poofed Lapis Lazuli. Apparently during this she also ended up coming across a herd of mammoths, deciding to practice her muscle by juggling a calf, which resulted in the herd attacking them. It is currently unclear how she ended up poofed, though it can be assumed that she was found by Rose, and put in Lion's mane for safety.
Bismuth was released thousands of years later inside the pocket dimension of Lion's mane, only able to get out when Steven Universe brought her out to show the others. Bismuth immediately gets comfortable with Pearl and Garnet, and is introduced to Steven, Fulgurite, and Amethyst, along with some of the ponies as well. She was given a refresher about the current state of their world, but not told about how they saved Homeworld yet, making her think that they can fight back and show them what they were made of. She went off to The Forge and started work on some weapons enhancements for the team, and later went to practicing these enhancements. That night, Bismuth got the idea to show Steven a better weapon than Rose's Sword, and she introduced him to the Breaking Point, a weapon that can shatter Gems easily. She began to get suspicious later though, and then accused Amethyst, Steven, and Peridot as traitors, trying to attack them and presumably kill them. She was only stopped when Quetzalcoatl showed up, though she still tried her Breaking Point, only for it to wreck itself on use on his scales. Only then did she learn about the Osicone, and what they did, but she took it as an amazing change, and adapted fairly easily to it.
Bismuth quickly became comfortable around everyone after this, though the only person she was having trouble with was Lapis Lazuli. She found her outside during the Hearth's Warming play, and she wanted to know why, only finding that she just needed some alone time.
She was more than willing to join the fight when Sapphire was taken away, and joined them as one of Lapis Lazuli's subordinates, and it was her who supplied the weapon enhancements needed for the team, to which she had Pearl hold for them. She went with one team to head to the prison hold, and ended up captured while trying to fight the Gem Hybrids.
As she was working with the others to build the Gem Drill, she met Kyra when he arrived for their aid, and with not much else to do without Jasper around, she went with them after building up a metal boot for Kyra's scarred hoof as a bit of a present. She actually hoped that the winter in Darastrix, for it would be a blast fighting a monster on Equus. when the Giant Bird showed up, she immediately decided to fight it, giving her friends time to get away sometime during the fight, though she actually got into a bit of trouble until Smoky Quartz helped her out. She helped in tracking down the bird the next day, and confronting Starlight Glimmer and the Giant Bird.
When Lapis Lazuli isolated herself in the barn, she tried to make her feel better by making her a pond right by the barn, though only finding that it didn't work the way she wanted it to.
Bismuth was brought to Homeworld for the trial, and she tried to help Steven out during it, keeping him calm. In the end, she was sentenced to banishment of Homeworld, which she took in stride as it was nothing new for her.
Bismuth's involvement in Season six is pushed aside for most of it apart from a few notable episodes:
In "Renegade Gem vol.2", Bismuth trained with Jasper one day when Flint left their group a letter on his tasks, though she quickly confirmed that he probably lied saying he told Garnet about it and got the greenlight.
In "The Sound of Silence", Bismuth's role became a lot more prominent, as she was one of the Gems brought to the meeting Flint held for Pearl's involvement. When asked if it was odd, Bismuth revealed that it had always been her "thing" to cover her mouth. She tried to defend Pearl, saying it was anyone's guess as to what she could've gone through during the Gem War, only to be pointed out she wasn't too involved in it herself. She joined Flint and Star Quartz the next day, unsure about it still and thinking perhaps it wasn't as bad. She and Jasper confront Pearl directly and ask about her involvement, though when she refused to speak, she puts it down to just shock. She and Lapis tell Flint a lie so he wouldn't bother her, and she went right to Pearl, trying to be the nicest she could about it, saying she trusted her with her gemstone. When Pearl's body began to retaliate, Bismuth tried to help and force her arms down, telling her to fight it and that she and Lapis were there for her. It didn't work however, and after she poofed herself, an angered Bismuth confronted Flint and asked if White Diamond would do something like this to her.
She quickly got captured along with everyone else, and she did end up being rescued by the humans.
Bismuth amongst the numerous others stranded on the Jungle Moon took shelter within the Jungle Moon Base until they would be rescued. During the stay in there, she and Lapis both were tasked with gathering more food for the Humans and the Ponies. It is revealed through a flashback told by Tiger's Eye that she, Lapis, and Tiger's Eye had gone to the Prime Kindergarten prior to being captured. She tried to be on good terms with Lapis throughout the entire mission, though during it she was told by Lapis to simply leave, as Lapis was bitter with her still. After the mission, and a chance encounter with the Injector Monster, she finally got Lapis's friendship. She is also one of the Gems who agreed to go back to the White Diamond Space Station to rescue Pearl, Aquamarine, and the Zooman and Zoomare.
After the revelation of Pink Diamond's true identity, she was into The Forge to create more weapons, namely a new sword for Connie Maheswaran as she lost hers thanks to White Diamond. After being told the whole story, she admitted that everything suddenly made sense, but she still stayed with them, keeping her promise to Steven she made since first meeting him.
White Diamond Arc
Bismuth joined Steven in going to Homeworld for a surprise visit not long after Steven's Birthday, her and the other Gems being "the pride of Lions" going into the "Lion's Den", and promising that everything will be alright. She didn't take kindly to White Diamond taking over Homeworld along with the others, She was the most defiant when hearing about Steven's plan to befriend White Diamond, at first refusing to go with him as she didn't want to place her Gem on White's Anvil. Despite her initial doubts, she joins them anyway under White Diamond's instruction, joining them on their trip to Heiligdom, Farid, and Orthix.
My Little Universe II
In With My Tanks, she and Flint arrive into the Strawberry Battlefield in order to keep an eye on Amethyst, Bismuth going as she was the only one who could stop the Crystal Tank if it had to come to it. While they were there, Bismuth expressed her joy for the history of the battlefield, though ended up extremely upset when she found how little Amethyst and Hessonite care about the place, and how much was being destroyed. Throughout much of the day, she spent it gathering the weapons from said Battlefield so they wouldn't get destroyed by the Crystal Tank, revealing that she still deeply cared about what the place meant as it was important to her, even if the Gem War wasn't what she originally thought anymore. She stayed overnight, and fought alongside Hessonite and Amethyst against Nichrome when he stole the Crystal Tank. Upon driving him away though, feeling distraught over the loss of the Strawberry Battlefield, she decided to leave them alone and just go home. She returns to Little Homeworld to find that her friends had decorated her new Forge with the old weapons, and were planning to make a museum commemorating her weaponry and the Gem War, much to her delight.
She joins the Harmony Gems in both the final court session with Discord and White Diamond and the final fight with Grogar's Army. Before the fight, she remains behind in the Realm of Corners to buy her friends time to destroy Grogar's ships. However, in the end she was captured along with the other Harmony Gems and Off-Colors, and brought onto the ships to kill them in front of Empire City. Lucky for her she was freed by the recovered Harmony Gems and with their help they stop Grogar's forces from leaving Homeworld.
Bismuth is known to have created multiple forms of weapon enhancements, and weapons in general, for the entire Crystal Gem army, as it was something she herself decided to do once she joined the Crystal Gems.
While not as prominent or as varied as Amethyst, Bismuth is shown to have a level of shapeshifting ability, mainly in her hands which she often turns into a number of items, such as hammers, a racket during a game, a roller when cooking, and most commonly an axeblade for combat.