Minax

Minax is the main antagonist of the video game Ultima II: Revenge of the Enchantress.

Ultima II
At some point, Minax became the apprentice to Mondain, the main antagonist of the first Ultima game. After his death at the hands of a person known only as the Stranger (who would later become the Avatar), she began to study the dark arts in order to further increase her power, and discovered that the Stranger was in fact not from Minax's home dimension of Sosaria, but rather another world called Earth. When the time was right, she used her powers to travel back to a prehistoric Earth where she created her base of power. She then used her abilities to manipulate history, eventually resulting in a nuclear holocaust that exterminated all life on Earth in the late 21st century.

Due to the magical artefacts retained from his/her time in Sosaria, the Stranger remained immune to the changes in the timeline and began to amass enough strength to destroy Minax, while also obtaining the only weapon capable of harming her, the Quicksword. Eventually, the Stranger travelled back to the era when Minax dwelled, and after penetrating the defenses around her castle attacked Minax herself. After a lengthy battle in which Minax continually teleported around the castle, she finally fell. With her death, the changes she brought upon the timeline were undone, and Earth's history was restored.

Ultima III
Minax is only mentioned briefly in Ultima III: Exodus, but is revealed to have helped Mondain create the titular villain, Exodus while she was still alive.

Ultima VI
Minax's second and final appearance in the series takes place in Ultima VI: The False Prophet, where it is revealed that the Gargoyle race took her soul (along with those of Mondain and Exodus) and imprisoned it in a statue designed to represent one of their three virtues. Minax was chosen to be the embodiment of Passion, and upon meeting the Avatar again, explained that it was her passion for Mondain which drove her to such lengths to avenge him. Unlike Mondain and Exodus however, Minax actually expressed remorse over her actions.

Trivia

 * Minax was both the only female main antagonist for an Ultima game, and the only antagonist from the series to actually attack Earth instead of the world of Sosaria, or Britannia as it would later be known (the Guardian threatened to attack Earth in the ending of Ultima VII and the opening cutscene of Ultima VIII, but never actually went through with it).
 * While the artwork in the Ultima II handbook and in-game art in Ultima VI both depicted Minax as an older woman, the Tapestry of the Ages seen in Ultima IX showed Minax being relatively young when she battled the Stranger. Given the numerous other continuity errors in the tapestry (not to mention the game as a whole), most fans disregard this depiction and accept the older version of Minax as canon.