Uilleam III of Ross, or William III of Ross, was the fourth successor of
Ferchar mac in tSagairt, as
Mormaer of
Ross (
1333/6-1370).
Uilleam came into his inheritance at a torrid time, his father
Aodh dying at the
Battle of Halidon Hill. Uilleam temporarily lost many of his lands. However, he returned from Norway in 1336 and regained them. Uilleam cultivated the friendship of the
Stewarts, and was rewarded by being appointed
Justiciar of Scotia. Uilleam's reign was marked by continued strife with his nominal vassal, Ranald MacRuadridh (Lord of
Skye). In
1348, Uilleam killed Ranald with eight of his men at the nunnery of
Elcho.
Uilleam married Màiri, the daughter of Aonghus Óg
MacDomhnaill. They had an heir, Uilleam, but he died in
1357. Uilleam's lands were forfeited by King
David II in
1370. Uilleam died in
1372, and the Mormaerdom was given to his daughter
Euphemia with her husband Sir
Walter Leslie, thus ending the dynasty started a century and a half before by the great Ferchar. The dominions eventually passed to the MacDonald
Lords of the Isles. 
