Two of them appear to play a part in the Escavalon episode of Chrétien’s Perceval.
The first discovers the king’s sister enjoying an obviously hot flirtation with Gawaine and, though Gawaine is universally hated in Escavalon for allegedly murdering its previous ruler, this vavasour is the first to recognize him and raise the alarm, summoning the mayor and magistrates to lead the mob.
It’s probably not the same wise vavasour, a native of that town and advisor to the country round, whom the young king finds in the square after dismissing the mob, and who advises him to postpone Gawaine’s trial by combat with Guigambresil for a year and meanwhile send Gawaine in quest of the Bleeding Lance.
See also
King of Escavalon | The Legend of King Arthur
Alderman of Escavalon | The Legend of King Arthur
Sister of the King of Escavalon | The Legend of King Arthur