The story of King Artoria differs from the real world story of King Arthur, although even the latter have a lot of variations. In the Fate series, there are bits and pieces of Artoria's life being revealed in each iteration of the game. But is there a complete story of the King Arthur story in Fate from beginning to end? Is her story even interconnected in each of the Fate works?
I have decided to edit this question to remove the huge quote text from the Wikia and sum it up in my own words. you can read up on the original from of this answer here
Artoria (or Arturia as the common mis-translation) was born during the war-torn Dark Ages after Britannia lost it's protection from the Roman Empire. During this time Uther Pendragon was the King of Britain and he had already fathered a daughter (Morgan le Fay) with the wife of the wife of the Duke of Cornwall, Igraine.
Merlin, an Human/Incubus Hyrbid and a powerful Magus, had prophesied that their next child would be Uther's successor as king and Uther believed this. However when Arturia was born Uther despaired as she was born a girl, not a boy. in those times a King could not make a child that was not male his successor even if she was fated to one day become a king. Merlin was delighted because the sex of the child had never mattered and he was confident that if Arturia was separated from the castle until the day of prophecy it would be proof that she would become king.
At the age of five, Arturia was entrusted to one of the king's vassals, Sir Ector, who while he did not believe in the prophecy he did feel the same air from the young Arturia as he did his king. Arturia was then adopted and raised with Ector's own son Kay training them both as simple knight apprentices.
Kay could tell that Arturia would grow up to be a beauty woman but his father told him to guide her like she was his brother and decided to treat her in that manner, though he did not believe it would be kept secret. Initially Arturia was raised under the belief that she and Kay were related by blood, but she was later told the truth while growing up. Despite this their relationship did not diminish from the truth, and they still felt they were true siblings.
Arturia acted as Kay's squire and received training from him while also doing other chores such as pulling along his horse. During their sparring Arturia was the greater in terms of swordsmanship however Kay would use "warped reasoning just on the verge of being correct" to make her feel like she had lost despite winning, reasoning like
- "You lose since you threw away your sheath!"
- "I'm still alive so don't act like you won!"
During one rainy day while Artoria was sick, Kay's mother had to leave so only he was available to tend to her. Telling Arturia "it would be troublesome for me if you were to die now", he promised to do anything she requested in exchange for getting well quickly. Being very persistent in having her request something Arturia said she wanted to "dream of a lion running across plains." To fulfill this Kay carved a wooden lion. The carving was poor as Kay was hoping to make an old, dying lion unable to hurt a mouse so as to not have it harm her in her dreams and Arturia compared it to a cross between a dog and a cat, but she appreciated it and was able to see the dream.
While being raised by Ector Merlin also visited teaching Arturia and acting as a sort of foster father figure to her. he also also revealed Arturia's gender to Kay making him swear to secrecy.
When Arturia was 15 the day of prophecy arrived and Merlin prepared Caliburn for the selection of the next king. when the Knights and Lords gathered for the selection of the next king they expected the selection to be through jousting to select the most superior one to become a king, but they were presented with Caliburn stuck in a stone with the inscription on the hilt reading
Whosoe'er pulleth out this sword of this stone is rightwise king born of England.
While many knights grabbed the sword trying to follow the command, none were able to pull it out. With no successful attempts they began the expected jousting to make the selection. at this time Arturia was still an apprentice and thus not qualified to joust. she neared the now deserted stone and reached out for the sword without hesitation.
Before grabbing it, Merlin appeared before her to tell her to think things over before taking it. He told her she would no longer be human upon taking the sword, but she had been prepared for the fact that "becoming a king means no longer being human" ever since she was born knowing that a king is someone who kills everyone to protect everyone, having thought about it every night and shuddered until morning came with not a day passing where she did not fear that fact. to Merlin her response was a nod saying that the fear she has felt would end then
Arturia pulled the sword out effortlessly as per her fate and in that instant She became something not human. to everyone else there so long as she acted like a good king no would care for her appearance of gender. Taking the sword also had an effect on her body stopping her from aging as such from then on the King would have a body of a 15 year old.
After that Arturia, Merlin and Kay went through various adventures while training eventually calling herself the rightful King of the country while reclaiming the country and the 3 of them formed the original Round Table but later was joined bu Bedivere and Gawain who along with Kay becomes the most senior knights.
At some point during their adventures Arturia came to care for a lion cub for a month. While she claims that it wasn't because she liked them (most probably due to the carved lion she was given by her beloved brother) she formed a bond with the young cub who had become attached to her. the lion cub was very energetic, often biting or scratching, but experiencing the happiness she felt from this she wished to be able to stay with the sub until the end. while it's not documented on when this occurred given the images we have seen of Arturia as King and in battle where she wears the same blue attire under her armor i suspect it was during this adventures due to what she is wearing in a flashback image in the Visual Novel
Morgan le Fay, who was born as the proper, recognized daughter of King Uther and Arturia's older sister of the same status, in her eyes believed Arturia received the love and hopes of their father that should have been hers, became witch queen who craved for vengeance. during their adventures Morgan executed a trap which saw Arturia loose Caliburn to which afterwords Arturia goes to Vivian, the Lady of the Lake (and Morgan's polar opposite).
After the final battle against her uncle Vortigern, Arturia claimed her kingdom Camelot and spent ten years in peace. during this time Arturia had to deal with the problem of being able to produce an heir. to "help" Merlin used his magecraft to make Arturia into a pseudo-male capable of producing sperm for an unknown duration of time. during this time however Morgan le Fay
got her sister drunk used her magic to enchant her sister to take some of Arturia's sperm. using her own ovaries Morgan developed the sperm and have birth to a homunculus clone of her sister. this was Mordred.
Arturia met the daughter of King Leodegrance, Guinevere, and the 2 wedded to make an outward appearance of a "kingdom" in Britain. They even held a grand wedding ceremony that lasted close to seven days and was celebrated throughout the land. However it was marriage out of necessity rather than love, where Arturia, the "husband" was not a man and the marriage would never be consummated.
During this time Mordred was raised by Morgan to believe it was her right defeat the King and inherit the throne. Through her mother's recommendations and a presentation of her own swordsmanship, was able to be counted as one of the Knights of the Round Table. despite her mother's obsessive hatred for Arturia Mordred never hated Arturia yet idealized her as the perfect king. she later learned of her heritage of being Arturia's "son" and was happy in learning that she shared the same blood as the king she idolized, however Mordred also felt ashamed of her twisted birth.
As Arturia continued to be king she kept to the oath that a king is not human and that one cannot protect the people with human emotions. never narrowing her eyes in grief while on the throne and settling every problem while working hard in government affairs, Arturia managed to balance the country without any deviations, and punished people without a single mistake. this however lead one of her Knight, Sir Tristan to leave Camelot saying
The King does not understand how others feel
hearing this Lancelot wished to lessen the burden for his King, a wish that Guinevere also held. While they conversed with each other they came to recognize each other as friends and rely on one another and it was then that Lancelot began to fall for Guinevere. it was though Guinevere that he learned of Arturia being a woman and the true meaning to Guinevere's marriage to her.
At some point in time Mordred approached Arturia about her identity and her "son" but rather getting the acceptance she had hoped for Arturia rejected her stating that while Mordren was her child born from her and Morgan's plotting she could not recognize Mordred as her "son" or give her the Throne. Mordred believed this however was because Arturia hated Morgan and no matter what she did, the moment she was born from Morgan she was a dirtied child and the shame of her birth began to become hatred.
Lancelot and Guinevere began to have an affair and this was discovered by Agravain, one of Arturia's Knights and an assassin hired by Morgan who he hated. Agravain was loyal to the King however he hated women due to Morgan and when he uncovered the affair he also learned of Arturia's true gender. he tried to threaten Guinevere with the fact of her affair but failed. before his death and seeing Mordred's growing hatred (while probably not knowing Mordred was a woman as well) he revealed the affair to her who used it to sow mistrust in the Knights of the Round Table and destroying the prestige of the King in the eyes of the people.
When Arturia learned of the affair she did not blame anyone but rather understood knowing Guinevere's and Lancelot's sacafrice. however still acting in the capacity of a king and this times adultery was a serious crime, Arturia discarded her emotions and had Guinevere executed. Lancelot tried to stop to save her, killing several of his fellow knights including Gawain's brothers, Gareth and Gaheris but ultimately failed and fled back to his homeland of France.
When Arturia left for the Rome expedition Mordred became the leader of the rebellion representing the national discontent towards the King. when Arturia returned Mordred raged and proclaiming her hatred of the king and that only she was fit for the throne. the truth was that she only wanted to be accepted by Arturia as her "son". this sparked the civil war that would later claim their lives.
shortly before the final battle of Camlann Avalon, the sheath to Excalibur that gave Arturia immortality, was stolen due to the machinations of Morgan le Fay. Lancelot, even after being excommunicated, wanted to participate in the Battle of Camlann to serve his King but Gawain hostilely rejected him due to his hatred.
Merlin left Arturia before the final battle because of his own love affair problems claiming that an evil witch (Morgan?) tried to murder him so he fled to the Reverse Side of the World and thus the land of Avalon where he thought the witch wouldn't reach him, however the gate he encountered was a trap which created a sealing "tower" called the Garden of Avalon and having transcended death, is trapped for all eternity and thus can never enter the Throne of Heroes.
During their final battle Mordred hated the "Son of Morgan" but Arturia replied
Not once did I despise you. There was only one reason I would not give you the throne. You didn't have the capacity of a King.
In their battle Mordred was fatally wounded by Rhongomyniad but because of a curse on her, after death still swung her sword and fatally wounded Arturia.
Arturia's dying body was escorted to a holy isle by Sir Bedivere where she ordered a grieving knight to dispose of Excalibur by throwing it back to the Lady of the Lake, an order he failed twice beliving that the moment Excalibur was returned to Vivian Arturia would die.
In Bedivere's absence, she reflected on her personal failures, regretting her life as king. Before her last breath, she appealed to the world; in exchange for services as a Heroic Spirit, she asked to be given an opportunity seek the Holy Grail to save her country.
i emphasize the last bit as after this is when Arturia made her contract with the world and started to be summoned to the Holy Grail Wars. unlike the other Heroic Spirits who are effectively clones of their real selves in the Throne of Heroes, Arturia never made it there which is why she can retain her memories of previous times she has been summoned.
after the events of Fate/Stay Night, depending on the route Arturia' fate different. i summarize it in this answer but to sum that up
- In Fate we see Arturia accept things when Sir Bedivere returns for the final time
- In -Last Episode- because Arturia terminated her contract with the World by destroying the Holy Grail by her own will she goes to Avalon in the Reverse Side of the World, waiting for Shirou who eventually reunites with her as apart of a miracle Merlin talks about
- In Unlimited Blade Works:
- In the Good End she remains with Rin as her Servant
- In the True Ending Arturia fades away however we don't know if her contract was terminated or not and if it was if she ended up in Avalon aswell
- in Heaven's Feel, regardless of the ending Arturia is corrupted by Angra Mainyu and is killed by Shirou close to the final battle. we don't know of her fate after this
- in Fate/Hollow Ataraxia she is summoned for Angra Mainyu false Holy Grail War. because Angra Mainyu was trying to recreate the 3rd war Arturia is summoned as if she was summoned by the Edelfelt sisters who used their sorcery trait to summon 2 Sabers (2 sides of the same Hero) Arturia is summoned with the ability to swap with her Alter personality (the Arturia corrupted by Angra Mainyu)
Also while we do not know when about in Arturia's own timeline this occured
- in Fate/Labyrinth she is summoned as Norma Goodfellow's/Manaka Sajyou's Servant during the Subcategory Holy Grail in Caubac Alcatraz's labyrinth. she forms a party with 3 other Servants, Archer (Robin Hood from Fate/Extra), Caster (Medea from Fate/Stay Night) and Assassin (Hassan-i-Sabbah from Fate/Stay Night). because of a fading contract with Norma/Manaka and the uses of her Nobel Phantasm during one battle Arturia fades away but not before saying her goodbyes to the other 3 Servants and entrusting them to give Norma/Manaka a Mystic Code she found
i would also add that at some point Arturia's Bloodline survived somehow as in other Type-Moon Works Lord El-Melloi II (Waver Velvet's name after the 4th Holy Grail War) meets with Gray who becomes his assistant. aside from her appearance being like that of Arturia which bring up unpleasant memories of the 4th Holy Grail War for Lord El-Melloi II Gray also can wield Rhongomyniad.
while not something special in itself Rhongomyniad is passed down through the generations with it's mystery preserved similar manner to the Tradition Carrier trait held by the Fraga family (Bazett Fraga McRemitz) which is passed down to a single successor from generation to generation through a pathogen in the Fraga bloodline. (similar manner as it's not know if there is a pathogen in Arturia's bloodline like that of the Fraga).
currently all we know is that Gray was born in a cemetery. we don't know from who she descends from or if the bloodline tied to Rhongomyniad starts from Arturia or from Uther (in which the bloodline could continue with Morgan who in the Nasuverse (according to the wikia) is Uther's daughter not the Duke of Cornwall unlike in other Arthurian Legends)
Sources (all the Type-Moon Wikia)