Angus is first introduced in volume 11 of the Hidan No Aria series and is shown to be the manservant of GIII. He is and old man and a frail one at that, out of all the members of the League he is the weakest. It isn't really known why GIII picked Angus to be his manservant but still even if he is the weakest his respect towards his leader (GIII) is just as strong as everyone else's.

Hidan no Aria Series
Tohyama Family
Holmes Family
Hotogi Shrine
Vlad Family
GIII League
Regiment Hex
Other Characters
Hidan no Aria AA
Yagate Maken no Alicebell