When the cosmic being Dormammu threatened Earth, Kaecilius betrayed the Masters of the Mystic arts and allied himself with Dormamu as his herald. As the Masters of the Mystic Arts began their battle with Kaecilius, many were killed in the process.
After Stephen Strange defeats Kaecilius and Dormammu, only he, Krugarr and Wong remain as Masters of the Mystic Arts. Thus, Strange fullfills his duty and his destiny to protect the universe from magical and cosmic threats, with Wong at his side and both using the New York Sanctu Sanctorum as their headquarters.
While most of the Masters come from Earth, both Topaz and Krugarr come from alien planets.