Euclid (エウクレイデス, Eukureidesu?), Class Name Foreigner (フォーリナー, Fōrinā?), is a Foreigner-class Servant summoned "After" the Holy Grail War in Fate/Requiem. Her unnamed Master is a teacher who works at an elementary school.
Euclid was a Greek mathematician. As a Servant she works at a large library called Alexandria in Tama. She and her Master don't normally stick together and do things separately, her Master using his Command Seals to allow her to move freely on her own.
Euclid is the only Foreigner-class Servant known to be summoned in Mosaic City. As a Foreigner, Euclid is bound to a creature outside reality. She chants "Iä! Iä! vulgtmm...vugtlagn...", which implies it is Hastur.
Euclid is a girl who wears a cloak resembling the Foreigner class card.
Euclid tends to refer to things as "Euclidean" or "non-Euclidean" depending on how she feels about them.
She is a bookworm who knows a lot outside her area of expertise, such as the connection between the French word "Élise" and Greek "Elysium".