Balbus is a Champion who can be found in the city's emergency barracks, located at the Circle of Trust Inn, in the Mardaneus Plaza district of Aleroth during the events of Divinity II: Flames of Vengeance.
He is responsible for Aleroth's wanted board which lists the city's most notorious criminals, so adventurers may seek them out for the thrill and the gold. You'll need to speak with him after slaughtering any of the miscreants for A Hunting We Shall Go Once More. As a special reward, he'll give you Caracalla's Warhammer if you manage to slay them all.
Balbus can be mindread for 22500 exp, revealing "What to do? If the Black Ring attack, I will surely need my Order of the Viper armour to survive... but the Dragon Knight could put it to better use than I... Should I part with it in this hero's favour?" This allows you to inquire about the Order of the Viper Cuirass, and he will tell you to "take it, wear it, make Aleroth proud!"