Martha, also known as Saint Martha, the Dragon Rider, a saint of the 1st Century who suppressed the evil dragon Tarasque. A holy maiden who made a terrible and grotesque monster fall madly in love.

Gilles de Rais summons various Servants to face Mash Kyrielight and Ritsuka Fujimaru, including Saint Martha, who is summoned as Berserk-Rider.

(Source: TYPE-MOON Wiki)