Master Aarindarius is a friend of Vaarsuvius's family and the person who initiated V in magic and tutored them. Aarindarius was an honorary Iron Mage in the Library Stadium. Aarindarius is implied to be extremely powerful, as Vaarsuvius imagined their mentor being able to effortlessly kill the Mother Dragon without even looking up from his book. If all assessments regarding this situation are correct, Master Aardinarius is almost certainly epic level character as Qarr recognized the Mother Dragon as an Ancient Black Dragon (Challenge Rating = 19) and so his level should be significantly higher than that.