Most civilizations made "magician" a word, which often translated as "illusion", from Mags. She (once a he) is a sneaky one that loves to perform illusions of people, often vanishing in less than a second in front of their eyes.
She often picks up people from all of time and space and takes them onto her TARDIS. If they did not catch on quick enough, she gently let them go.
Mag often stayed on Gallifrey until about 50 years before the time war (first incarnation). She took a trip away from the planet, when her father told her to, knowing what would be coming. Not knowing what was going on, Mag went to earth and stayed there until 2000, when she traveled back in time to the 1940s (second incarnation). She stayed there until unknowingly and supposedly, all of her race was dead. She did not know about the Doctor, and so went off on her own adventures with her own companions.
Mags got an idea from one of her companions, (who has no idea what was going on) to find a new planet that is supportive of time-lord life. She took an army ("borrowed" from WWI) and fought the native citizens (third incarnation). She finally claimed the place and named it "Gallifrey II" or "New Gallifrey". She has been building there and living there, often traveling back to Earth, especially in recent times (fourth incarnation).