An evil warrior in Heinrich von dem Türlin’s Diu Crône.
His companion, Lohenis of Rahaz, stole Gawain’s horse. Ansgü, knowing that Gawain had replaced his warhorse with a nag, challenged him to a joust.
Gawain was victorious despite the disadvantage. Ansgü’s counterpart in Wolfram von Eschenbach’s Parzival is Florant of Itolac.
Source
Diu Crône | Heinrich von dem Türlin, c. 1230