Marmaduke m
English: of uncertain derivation. It is generally held to be an Anglicized form of the Old Irish name Mael-Maedóc ‘devotee of Maedóc’. The name Maedóc was borne by various early Irish saints, most notably a 6th-century abbot of Clonmore and a 7th-century bishop of Ferns. Mael-Maedóc Ó Morgair (1095–1148) was a reformer of the Church in Ireland and a friend of Bernard of Clairvaux. However, the modern Gaelic form (from c.1200) is Maol-Maodhóg (pronounced /mʌl'məƱg/), so that the name would have had to have been borrowed into English before this loss of the d. Marmaduke has never been common except in a small area of North Yorkshire, and is at present almost completely out of fashion.
First names dictionary. 2012.