Maccus is a personal name which is first attested and possibly coined in the tenth century, the name Maccus, later also written as Mac(c)hus, was especially common in the Border country:
For a discussion of the origin and development of the name, see David E. Thornton, "Hey Mac! The name Maccus, tenth to fifteenth centuries." Nomina 20 (1997-9): 67-94, with appendix by O.J. Padel on Talkarn Mackus, 95-8.