Mordred, the Knight of Treachery, is a homunculus clone created by Morgan le Fay. Morgan used magic to extract genetic material from Artoria Pendragon while Artoria was magically altered to present as male. This origin granted Mordred near-identical physical traits to Artoria but also an accelerated growth rate and shortened lifespan. Raised secretly by Morgan, Mordred concealed her identity and obeyed the king until the appointed time to claim the throne as Artoria's heir.

Initially, Mordred held profound admiration for Artoria, viewing the king as a perfect ruler and knightly ideal. This devotion drove her to join the Knights of the Round Table. There, she demonstrated exceptional swordsmanship and upheld chivalry, masking resentment behind a helmet gifted by Morgan that hid her gender and lineage. Later, Morgan revealed Mordred's parentage, falsely claiming Artoria would reject her as "Morgan's filthy child." Instead, Mordred felt pride and sought recognition as heir. Artoria refused, declaring Mordred lacked the capacity for kingship—a rejection that twisted Mordred's devotion into seething hatred.

This hatred ignited rebellion. While Artoria campaigned in Rome, Mordred exploited growing discontent among knights and populace to seize Camelot. The conflict culminated on the hill of swords at Camlann. After a fierce duel, Artoria impaled Mordred with Rhongomyniad. With her helmet shattered, Mordred reached out, uttering "Father" before dying. Bound by a curse, her final strike mortally wounded Artoria, cementing Mordred's legacy as the Knight of Treachery who ended Arthurian legend.

Within the *Divine Realm of the Round Table: Camelot* singularity, Mordred serves the Lion King, an alternate Artoria. She guards a desert fortress, suppressing rebellions, capturing Hassan of Serenity during a village attack, and defending against invaders. Her loyalty here appears uncomplicated, lacking direct confrontation over past grievances. During the final assault on Camelot, she attacks Ozymandias' pyramid but is defeated by Xuanzang Sanzang.

Mordred's personality is defined by explosive rage, pride, and a volatile mix of love and hatred for Artoria. She reacts with hostility to questions about her gender or origins, yet shows no discomfort in revealing modern attire like a crimson leather jacket and tube top. Her combat style is brutal and unrestrained. She wields the stolen sword Clarent. Her Noble Phantasm, Clarent Blood Arthur ("Rebellion Against My Beautiful Father"), unleashes crimson lightning, requiring her to remove her helmet—an act representing both defiance and exposed identity.

Beyond Camelot, Mordred's significant portrayal is in *Fate/Apocrypha* as "Saber of Red," summoned by Master Kairi Sisigou. Her wish for the Holy Grail is to revisit Camlann and prove her worth to Artoria by pulling Caliburn. Her dynamic with Sisigou reveals loyalty beyond her Artoria obsession; she chooses to fade alongside him after his mortal injury rather than find a new Master, preferring straightforward individuals who respect her autonomy.

Mordred's design features full-body armor concealing her gender, contrasting with a civilian outfit of a white tube top, red leather jacket, and shorts highlighting her athletic physique. Her face closely resembles Artoria's, with sharp features and blonde hair often tied in a bun. As a *Fate/Grand Order* Servant, her abilities include "Mana Burst" for enhanced attacks, "Secret of Pedigree" for defense and debuff removal, and "Knight of Red Lightning" for increased critical damage. Her Noble Phantasm deals area-of-effect damage with added potency against Artoria-aligned enemies.

A summer variant, "Rider Mordred," appears in seasonal events, wielding a surfboard as a Noble Phantasm. This version retains her core traits while adopting a more lighthearted demeanor.