The Mutant-Master was an alien from star-sun Sirius that intended to cause nuclear war between the US and the Soviet Union, which would wipe out the human race, and he uses his Factor Three
organization to try it. After Changeling
discovered his plans to destroy mutantkind as well as humankind, he helped the X-Men to defeat him. Banshee destroys Mutant-Master's cloaking device, and reveals his alien appearance. Then the X-Men and the remainder of Factor Three joined forces in attacking Mutant Master, who committed suicide to avoid capture, during X-Men #39
The Mutant Master had no powers of his own, relying on equipment. His weaponry included lasers, explosives, sonic weapons and a force field.