Who is Angus McDonald from Mercy and what is their importance?

Angus McDonald is Cam's uncle. Angus is the last in the line of men who were left to watch over Carrymuir when the McDonald clan left Scotland. Angus was still living in Carrymuir when Cam went to him to ask him to take the role of clan chief. However, Angus refused the role, saying it was tradition that Cam take it and it belonged to no one else. Cam finally relented, taking his inherited role, under the condition that Angus returns to Wheelock with him. Angus agreed, leaving Carrymuir in the hands of the Scottish Trust. Now Angus is an old man, living out his days as the local dogcatcher.