Heroic Spirit of the bow. A type of Servant that has low basic parameters, but makes up for it with Skills and Noble Phantasms.
Of course, the Archer in the story was no exception, fighting to the bitter end while freely making use of unknown Noble Phantasms.
He is a thoroughly pragmatic cynic, but oddly enough, he also has a childish streak to him that makes him impossible to truly dislike.
His true identity is XXX. He is important enough to be considered a shadow protagonist, and it could be said that half of Fate/stay night is his story.
At the beginning of the game, his memory was supposedly fuzzy due to an imperfect summoning, but in reality that was only partially true.
The night he was summoned (after Rin went to sleep), he assessed the present situation, figured out his circumstances, and concluded that the opportunity to complete his objective had at long last appeared.
However, he didn’t realize the girl who summoned him was Tohsaka Rin until she introduced herself. (His memory wasn’t fuzzy, the name “Tohsaka Rin” had simply been worn away by time.)
At that moment, it all came rushing back like lightning.

“Then I’ll call you Rin. …Yes, it suits you well.”

Archer’s murmur at that time was thick with a heartfelt and madly passionate affection.
…By the way, there was lots of vague foreshadowing about Archer’s identity throughout the game, but none was more subtle than after the battle with Berserker in the Saber route.
Also, his skin was darkened from the rebound caused by using a certain spell… well, that’s the story, anyway.

Fate/side material: Fate Encyclopedia

Archer-class Servant summoned by Tohsaka Rin in the Fifth Holy Grail War. Conceited realist with a taste for sarcasm. An offhand remark about how it would be interesting if Archer was found in the red cellphone is what led to us creating the drama CD. Takeuchi Takeshi was the first one to make the suggestion.

HibiChika Complete Capture Book: Mahou Tsukai no Hako Small Encylopedia

Archer is one of the main Servants that the protagonist contract.
Enveloped in his red cloak, he is a young man in his mid-20s.
Despite belonging to the Archer class, he is a tough-as-steel Heroic Spirit and usually engages in close quarters combat. He is sometimes referred to as Koucha1, or even Red Archer in order to avoid being confused with the Archer who wears green clothing.
Archer usually uses the personal pronoun 私 (watashi), but depending on the situation he lets オレ (ore) slip out from time to time.

Having been introduced in Type-Moon works countless times, he is a very familiar Servant.
He is a cool-headed cynic, but he is also helpful and caring. Due to his character he is said to be a Servant who is also suitable to serve as a butler. Archer’s origin differs from that of other Heroic Spirits, and he cannot be considered a legitimate Heroic Spirit.
Archer is a guardian. He was born into the world as a kind of defense mechanism which arose from the collective unconscious desire of mankind for continued existence.
He was essentially unconsciously elected by the masses to be their faceless representative.
He carries out his mission as a guardian following a simple rule, “If some evil appears that threatens to speed up the collapse of mankind, I will eliminate it and all accessories.”
He crushes threats to mankind that the masses don’t even know or realize exist. He is, so to speak, a repairman of the ages. If there were ever a time without Archer’s deterrent power at work, destruction would rapidly spread and mankind would soon find itself facing an inevitable “END.”
Please refer to the EXTRA game contents to find out why this Heroic Spirit became one of mankind’s guardians.

Archer is a calm, collected professional, and he never lets his personal feelings interfere. He is always making a stern face, however this is probably due to his lack of freedom.
Although he takes up his role as a knightly bow-wielder, he was originally an old world magus.
He uses Projection Magic, which is the ability to replicate an object just by imagining it for a few minutes. He is a faker that can reproduce many famous swords.
The reason his main weapon is a bow is thought to be because he isn’t that strong of a Heroic Spirit, so he settled on ranged combat as his ultimate combat style.
In EXTRA Archer is almost the same entity as the Archer in Fate/stay night (although not the same person), but their true names are different. Please refer to Archer’s Special My Room in EXTRA to find out why his true name is just a regular noun, and not a normal human name.
Unlike Cas-Ko, Archer’s Special My Room is very simple to access. You can activate all his flags by talking to him in between rounds, Ms. Shirano.2

In CCC Archer appears as a half-naked perv— I mean… he is stylishly donning a red leather jacket. In CCC he is somewhat of a scoundrel, but nonetheless still reliable.
Even when he is on the far side of the Moon he coolly and wildly grasps the situation and helps out the amnesic protagonist. Sometimes he can be quite the nagging instructor.
In CCC his rival is Meltlilith.
If you choose both the female protagonist and the Servant Archer, the contents of Meltlilith-related events change completely.
Also Archer is the only Servant whose END differs from the rest.
The Servants based on Saber feature “The Future that begins in the Present,” while Archer features “The Present that begins in the Future.”
The reason for this can surely be understood by those of you who have fought to the end alongside Archer. I’m sure you understand without me putting it into words.

Translator’s Notes
  1. ^ Literally “red tea.”
  2. ^ This Ms. Shirano seems to be an inside joke. Maybe someone called Shirano sent them a fan letter asking how.
Fate/EXTRA Material: Encyclopedia of Fate/EXTRA

A mysterious Servant who controls a large number of rifles. Befitting the name Archer, she boasts incredible power when fighting from a distance, but the fact that she’s usually supposed to consume great amounts of mana makes her a difficult Servant to use. However, due to certain reasons, the problem of her mana consumption has been resolved.
One would not be able to tell from her appearance, but her true identity is that of the Demon King of the Sixth Heaven, Oda Nobunaga.

Fate/type Redline: Fate/type Redline Glossary