Heroic Spirit of the sword. A type of Servant that requires above average abilities in every basic parameter except for MGI.
Also, one of the main heroines of the story. A maiden knight that formed a contract with Emiya Shirou and fought to the very end of the Holy Grail War.
Her personality is righteous and thoroughly serious, and any sort of femininity she might have had has long since been usurped by her pride as a knight.
…However, if you strip away that veneer, a girlish aspect befitting her age will reveal itself.
She holds grudges when she’s sulking, and gets so sucked into competitions that she totally forgets about her surroundings. She gets overly excited about delicious food, and frets about making mistakes in front of the person she likes.
Honestly, she’s a hard to please heroine, umu.
Her true identity is King Arthur.
She disguised herself as a man to become king and brought peace to her homeland, but afterward lost her life during a civil war that tore her country apart from within.
The King Arthur in Fate/stay night is treated as a fusion of myth and historical fact. Her name before becoming king was Artoria.
Living in the castle while hiding her gender was an endless string of stressful situations. The matter of producing an heir was particularly troublesome, but it seems that she managed to get by without any problems thanks to Merlin’s spell. In the story, when she said that “she knows how to please a man,” she was speaking from actual experience.
She stopped aging the moment she pulled the sword of selection, so physically she’s about a year younger than Shirou.
Also, King Arthur is the red dragon that protects Britain.
Due to an arrangement her father, King Uther Pendragon, made with Merlin to produce an heir bearing the essence of a dragon, Artoria was born as a human infused with a dragon’s magical energy.
Consequently, she has no need for magic circuits. Her every breath, the very circulation of her blood, it all naturally generates magical energy. It wouldn’t be wrong to call her very being a “magic reactor,” on a completely different level from magi.
———Fate/stay night was originally her story.
At its conception, the main themes revolved around King Arthur and the Holy Grail, and that fact alone has never changed.
A maiden knight who galloped through the Holy Grail War.
I want to believe that the dream she saw at the very end was one worthy of her life.

Fate/side material: Fate Encyclopedia

A symbol-like existence. Without her, Fate wouldn’t be Fate. However, in Fate/Zero her kingly shell is still intact, and she plays the role of a hero instead of a heroine.
Over the course of Zero she experienced neglect play and tentacle play, was stalked, slandered, leered at, and preached at by drunks, and to top it all off the scoundrel who ambushed her at the very end turned out to be a former ally. It’s no exaggeration to say that the entirety of Zero is built on her suffering. Still, all of that was for the sake of enjoying Shirou’s delicious cooking ten years down the line. Or at least, that’s the excuse I gave to the Saber Maid figure that silently watched over my furious writing every day. If it had been the plain clothes version, I definitely wouldn’t have been able to finish the story. Even just seeing one in a store window was enough to make me drop to my knees, ashamed of my own ugliness, and yell to the heavens, “What kind of man am I, bullying such a pure and beautiful young girl like this!?”
By the way, about Saber’s suit. When I first imagined it, for some reason I just naturally assumed it would be a tuxedo. But after the art actually came in, I ended up settling on the current not-too-mannish traditional suit. Thinking about it now, making her patrol around a rustic suburban city like Fuyuki in full party dress would have been extraordinarily embarrassing for her, so it was probably the right call.

Fate/Zero material: Fate/Zero Encylopedia

Saber is one of the main Servants who can be contracted by the protagonist.
Her body is wrapped in a bright red dress. However she is a self proclaimed cross-dressing young swordswoman. She is often called Red Saber in order to differentiate her from the other Sabers.
She refers to herself with 余 [yo] or この身 [kono mi – literally: this body]. She only uses 私 [watashi] after she has lost her position as Empress.
When contracted by the protagonist she refers to his/her as 奉者 [sousha – literally: player].
Red Saber never lets her personal feelings interfere, and only at times when she must make use of her sword does she call the protagonist Master.
When alone and talking as a young maiden she refers to them with そなた [sonata].
By the way, the only one Red Saber ever says そなた [sonata] to during the Holy Grail War is the protagonist.

Red Saber is a self-proclaimed genius who is talented in everything. She is a selfish Empress who can realize almost anything she wants (through force).
She is often misunderstood and thought to be a tyrant because of her arrogant attitude and extremely confident way of speaking, however she usually acknowledges each individual’s unique way of life and does not deny the lives of people who are different from herself.
Red Saber doesn’t judge others based on social standards of good and evil, her standards revolve around the beauty of a person’s existence.
She has tried her hand at most fine arts including writing plays, songs, painting, and sculpting.
After completing a new work she begs for approval with teary eyes:
“What do you think of this? It’s quite good don’t you think? It might be a bit on the unique side of things, but it’s good nonetheless, right?”
As you can see, she is like a child who seeks attention.
Her parameters and stats don’t make her good enough to be a Saber class Servant, but she somehow managed to snatch Saber class with her Imperial Privilege. Properly she should be a commander-type Servant.

Red Saber has no particular wish or desire as a Servant.
Why? Well that’s because she is already perfect simply by existing.
At least, as Red Saber likes to say:
“I am complete just with my thoughts, my words and speech, and sleep. Regardless of what era I’m in, I will always be as such. This in itself symbolizes the authority and power of Rome.”
She is already perfect, so there is nothing more to wish for or desire.
She has the philosophy that simply being herself is the greatest reward of all.
She has unshakable, absolute beliefs and values within herself, so she doesn’t feel the need to oppose whatever is happening around her.
The one thing that Red Saber can never accept is acting in a manner that is unlike herself or not true to her values.
The egocentric Red Saber can accept becoming a Servant because being a contracted Servant is part of proving that she is the strongest.

“Hm? You desire that I prove I am the best?
I see nothing wrong with that. I simply will fight so as to not shame myself. To speak vulgarly, even if my Master was a frog, I would still fight alongside that frog to victory, as long as it is in a manner in which I do not shame myself, it would certainly be a great honor to me.”

She is a very positive thinker.
This is why it’s rare for her to scold the inexperienced protagonist. Although she is surprised at and complains about the protagonist’s timidity and frailness, from the bottom of her heart she isn’t looking down on him/her.
“So frail” and similar remarks are actually, as far as Red Saber is concerned, just honest appraisal.
So when the protagonist improves as a Master, and the trust they feel for each other deepens, she is able to be affectionate in a more direct manner.
“Oi, you need to pay more attention to me!
I’m the one with whom you have a contract, so you shall put me before all others!”
This is how the attention-starved puppy Empress who really, really wants you to pay attention to her came to be.

In the first place, however, there is no Master who wants to summon her.
Her true name is the same as that of a great evil in a certain religion, and her life ended in a wretched, miserable manner.
At once Red Saber is an Empress, and an artist who has no doubt about her own genius talent. To her absolute justice is only “beautiful things.”
Whether ally or enemy, her citizen or herself, she refuses to love anything that doesn’t fall under her definition of beauty.
Masters are, of course, subject to the same treatment. Red Saber will never obey someone who fails to meet her criteria.
It goes without saying that there is no magus who would want to employ a weapon that judges all things based on “beauty.” There’s just too much risk involved in contracting her.

“…Well, that’s only to be expected.
Magus are wise, and very calculating people.
There is surely no one so stupid as to trust in me.”

These are the thoughts of Red Saber who spent many idle, boring days in the Throne of Heroes.
Although lonely, her high pride won’t let her settle for just anyone, and she plans on only contracting with a genius who is on her level.
And so, at the end of the umpteenth Preliminaries, as she was about to leave the Servant selection room, thinking that once again there was no one who would call her name, she heard a small voice.
When she turned around, she saw someone on the verge of death trying to stand up, a person whose name she didn’t know.
Not strong in the slightest.
No outstanding talents.
Not even a qualified magus.
But…there was a kindling flame that refused to fade like a star in the pitch black sky.
She immediately rushed over.
In her heart she held no sympathy for the figure prostrated on the ground, rather her heart was filled with anger against the heavens.
Because she was someone who was rejected as a hero, she knew that it was the way of the world for the weak to disappear from the world with their prayers left unheard.
It’s precisely because she knew this truth that she couldn’t stand the heavens that would abandon such a strong desire.
The figure on the ground was on the border of death, yet still didn’t give up and chose to fight on.

“If the heavens won’t answer the impeccably pure wish of this poor soul, the will of the heavens is no longer of any matter!
How could I not answer the cry of that noble soul!”

As such, Red Saber was not summoned by a Master, instead she imposed her own will on the Servant selection room.
Despite hating settling for something other than a genius of her level to the point that she had a splitting headache, she still asked the nameless person the following:

“Answer me———are you my Master [sousha]?”

In CCC Red Saber appears wearing a white bridal dress.
Earning her the loving nicknames of Saber Bride and/or Wife Saber. Seeing as there is now another Red Saber in Fate/Apocrypha I feel like we need to think of a nickname in common for the EXTRA and CCC version(s) of Red Saber. Tange Saber…no? Yeah, I guess not.
Her rival in CCC is Red Lancer.
I hope as idols they can become good friendly rivals. Seeing as both of them have a pretty terrible past, they can probably share and their troubles and confide in each other.
Another thing to note is that the voice line Red Saber says when you acquire the swimsuit item is a must-hear. That line, more so than any other line, is said by Tange Saber in a way that will make you fall for her.

Fate/EXTRA Material: Encyclopedia of Fate/EXTRA

The Saber Servant that made a contract with Kanata. A Servant specialized in close-quarters combat that possesses both immense skill and agility. She also possesses an extremely powerful trump card that allowed her to erase the space between her and Archer, who fought at long range. Due to the fact she wears that extremely famous haori, figuring out her identity was easy, but Archer still has no idea who she is, so she couldn’t figure out her name.
Usually, Saber’s considered the strongest class due to having the best overall stats, but it would seem that in her case, her base stats are actually quite low.

Fate/type Redline: Fate/type Redline Glossary