Borg Queen

The Borg Queen is the Hive-Leader of the Borg and, like the Gravemind or the Dalek Emperor, is considered the highest rank of her species and conducts all tactical and operational planning for the race as a whole.

Her very existance was unknown to the Humans until the Human-Borg War, in which she revealed herself in an attempt to conquer Earth personally. Since the Borg were suddenly beginning to lose in their war against the Cybermen, the Borg Queen felt it necessary to oversee the destruction and assimilation of the Human Race personally.

However, she underestimated the crew of the USS Enterprise who were defending the Earth and destroyed her Borg Cube. She was able to beam aboard the ship with a small Borg taskforce who began assimilating the crew, but the combined fighting skills of Warf, Data and Riker were able to drive the Borg off and the Queen was eventually killed. Her death led to the Borg losing both their war against the Humans and their war against the Cybermen.