From the Latin name Marcus, borne by the Evangelist, author of the second gospel in the New Testament, and by several other early and medieval saints. In Arthurian legend, King Mark is the aged ruler of Cornwall to whom Isolde is brought as a bride by Tristan; his name was presumably of Celtic origin, perhaps derived from the element march ‘horse’. This was not a particularly common name in the Middle Ages but was in more frequent use by the end of the 16th century.
English (of Norman origin), French, and North German: from Giselbert, a Norman personal name composed of the Germanic elements gīsil ‘pledge’, ‘hostage’, ‘noble youth’ (see Giesel) + berht ‘bright’, ‘famous’. This personal name enjoyed considerable popularity in England during the Middle Ages, partly as a result of the fame of St. Gilbert of Sempringham (1085–1189), the founder of the only native English monastic order.