 Gummarus was assumed to have been a close companion of the Christian missionary Rumbold of Mechelen, who worked in Brabant, and is sometimes credited with helping Rumbold found an abbey at Lier.For this reason they are often depicted together in paintings and stained glass windows.However a 2004 examination of relics believed to be those of Rumbold suggests that he likely died over fifty years before Gummarus was born, so they would not have been contemporaries.