Empress of the Racnoss (The Runaway Bride)

The Empress of the Racnoss was the leader of the Racnoss Empire, an empire destroyed by the Gallifreyans over 4.6 billion years ago. She was the only Racnoss to survive and not hibernate in the Earth's core, but instead thrived in her ship, the Webstar, orbiting Earth for billions of years until the Torchwood Institute developed Huon particles with which she could revive her race.

The Empress was encountered by the Doctor on Christmas Day 2007 in a secret location under the Thames Barrier, trying to awaken her long-dead race (whom she called "her children") with the Huon energy within the bodies of Donna Noble and Lance Bennett after being fed it within drinks, being given coffee and water respectively. Lance was originally affiliated with the Empress, however after the disappearance of Donna after being taken by the Doctor she sent Lance to the centre of the Earth where the Racnoss spaceship was, and the Huon particles awoke the Racnoss who then proceeded to feast on Lance.

Her plans to revive the Racnoss were foiled by the Doctor when he used controls stolen from a Robot Santa to stop the Santas shooting him and to bring bombs disguised as baubles from a Robotic Christmas Tree flying around the secret room and then detonating, crashing into pipes, thereby letting the Thames flood into the room and surrounding the Empress with fire, and then finally drowning the Racnoss with the Thames water.

The Empress then transmatted up to her Webstar and vowed revenge on the Doctor and all of planet Earth by scorching it, however the lack of Huon energy left the Webstar defenceless and allowed the British Army to destroy it, presumably destroying both the Webstar and the Empress. (DW: The Runaway Bride)

In an alternate timeline, the encounter between the Doctor and the Empress ended differently. Although she was still killed, the Doctor also died, leading to a chain of events that drastically altered Earth history. (DW: Turn Left)