A Welsh bishop who King Mark commissioned to conduct an ordeal in which Isolde would have to prove her fidelity (chastity test).
On the way to the ordeal, a “beggar” (Tristan in disguise) helped Isolde cross a patch of mud, and Isolde was able to swear before God that no man had come near her except Mark and the “beggar”.
Source
Saga af Tristram ok Isodd | 14th century