Saber's True Name is Charlemagne (シャルルマーニュ, Sharurumānyu?), leader and namesake of the Twelve Paladins of Charlemagne. The legend of Charlemagne and his paladins is based off of the real life exploits of Karl der Große. They are both the same Heroic Spirit with the same Saint Graph, but Charlemagne would normally never be summoned due to the real life exploits of Karl far outweighing the fantasy. He is only summoned due to the specific events of the story, but his Saint Graph is registered as a unique existence at the end of the story to allow him to be summoned individually.
Charlemagne appears as a young man with black and white hair and blue eyes. His attire consists mainly of a black and white tunic with blue accents, black pants, thigh-high armored boots, and a short white cape with a black edge. Aside from his boots, his left arm has a gauntlet, and he wears a set of faulds at his waist. A sword scabbard hangs at his left side, and red marks coat his right gloved arm. He bears a resemblance to the historical Charlemagne during his youth, (more specifically when he first became a knight at and received his legendary sword Joyeuse), but has black/white hair in place of his recordedly said to have been brown or blond hair.
A carefree young man who somewhat bluntly says that he himself is not very suitable to be king. He places an aesthetic standard and behaviour on “whether this is cool or uncool”, even if that will be a handicap for the Master, or even a handicap to himself… Despite this personality flaw, Astolfo describes Charlemagne as a conscientiously benevolent king that would weep and laugh with his people and also help those who are in need.
Along with his main weapon, the sacred sword Joyeuse, Charlemagne is shown to be able to use the weapons of the Paladins due to his Holy Knight Emperor skill, like a serrated long sword, a halberd, a mace, Trap of Argalia, and has six red and six blue winged, javelin-like weapons floating behind him, that unleash multiple colored blasts.
Holy Knight Emperor (聖騎士帝, Seikishitei?) is a title skill bestowed to Charlemagne as the one who leads the holy knights (paladins) known as Twelve Peers. It provides a tremendous Charisma, improved attacks against the demonic, improved defences against Divinity, aptitude for weapons of the holy attribute and others. Also, this skill makes possible to invoke the Noble Phantasm, Joyeuse Ordre.
Mana Burst (Light) (魔力放出（光）, Maryoku Hōshutsu (Hikari)?) is a subspecies of Mana Burst that is allowed only to saints, holy maidens, and holy knights. It endows Charlemagne with an advantage against the evil aligned.
Over the Royal Road (王道踏破, Ōdō Tōha?) is a self-admonition type skill that displays its effects by having the user stick to the attitude of wanting to be a king. It contributes to the improvement of a portion of their parameters, but weakens them upon taking a conduct that violates that kingship. In Charlemagne's case, this means that he "gets weakened when doing something lame" and that "some sort of gauge rises when doing things that he finds cool".
His sword, Joyeuse (聖剣ジュワユーズ, Seiken Juwayūzu?), is a Noble Phantasm which is also possessed by Karl der Große. Unlike Karl, who is rooted in history rather than fantasy, Charlemagne is able to use it to its full potential.
Joyeuse Ordre: Exemplify the Heroic King, O' Twelve Radiant Swords That Travels the Wide World (王勇を示せ、遍く世を巡る十二の輝剣, Ōyū wo Shimese, Amaneku Yo wo Meguru Jūni no Kō Ken?) is a Noble Phantasm which is enabled through Charlemagne's position as leader of the Twelve Paladins and his possession of the Skill Holy Knight Emperor. It unleashes the power of Joyeuse and the weapons of the Paladins, firing simultaneous beams from all weapons against enemies.