Altria Pendragon is the legendary King of Knights from the chronicles of Britain, a figure rooted in the tales of King Arthur. In this interpretation, the once and future king is a woman who concealed her gender to rule and lead her people. Born the daughter of Uther Pendragon, she was raised by Sir Ector under the name Artorius alongside his son Kay. At fifteen, she fulfilled the prophecy of Britain’s rightful ruler by drawing the sword Caliburn from a stone, an act that halted her aging and made her a symbol devoted solely to her kingdom’s welfare. She brought an era of temporary peace and prosperity to a war-torn Britain, wielding the holy sword Excalibur, and established Camelot with the Knights of the Round Table. However, internal strife, including betrayal and the rebellion of her knight Mordred at the Battle of Camlann, led to her mortal wound. She carries the tragedy of her reign with the quiet dignity of a sovereign who gave everything for her nation.

Personality-wise, Altria embodies the ideal righteous king: stoic, serious, and unfailingly earnest, with the discipline of a model student who adheres to a strict moral code. Her life as a king conditioned her to behave in a manner befitting a male ruler, making her reserved and somewhat inept at handling overt romantic affection or being treated simply as a woman. Despite her composed exterior, she has a fiercely competitive nature and hates to lose, revealing a passionate spirit beneath her regal armor. She prefers simple, hearty meals over elaborate cuisine and has an unexpected fondness for stuffed animals, particularly lions.

Her motivations are driven by an unwavering sense of duty. Having witnessed the ruin of her homeland, she is a champion of the weak and believes that the role of a ruler is to lead the powerless. She has been summoned as a Servant in multiple Holy Grail Wars, where her wish for the Grail was to undo Britain’s destruction by selecting a different ruler. In other contexts, she is summoned to protect the future of humanity, fighting to correct anomalies in history without seeking personal glory. Her relationship with her Master is that of a loyal and respectful retainer and advisor, offering counsel based on her vast experience as a leader.

In darker circumstances, she can be corrupted into a version known as Saber Alter—a colder, more tyrannical figure who wields the corrupted Excalibur Morgan and rejects her past ideals. In a comedic setting, she appears as Mysterious Cat X in lighthearted segments that contrast her usual solemnity. She is also central to a phenomenon where many characters resemble her due to shared designs, including alternate selves and unrelated figures.

Altria is an exceptionally powerful Saber-class Servant. Her physical parameters are remarkably high, and her skills include a high rank in Magic Resistance that nullifies most magical attacks, the Riding skill allowing her to pilot nearly any vehicle, Mana Burst to release magical energy for enhanced power and defense, and Charisma that boosts the offensive capabilities of her allies. Her ultimate weapon is her Noble Phantasm, the holy sword Excalibur, a divine construct forged by the planet. By channeling immense magical energy into the blade and releasing it as a devastating beam of light, she can destroy fortresses and annihilate armies in a single strike. As Saber Alter, she uses the corrupted Excalibur Morgan. Post-upgrade, she also gains the Dragon Reactor Core, which temporarily converts all her attacks to a more powerful type and amplifies her Noble Phantasm damage.