Empress of the Racnoss (Donna's World)

On 25 June 2007, Donna Noble turned right instead of left; this small change in affairs produced Donna's World - a world in which she never met the Doctor. (TV: Turn Left) The Empress of the Racnoss (TV: The Runaway Bride) was confronted by a lone Tenth Doctor. He flooded her lair, stopping the Empress but apparently drowning himself in the process.

Biography
On Christmas Eve 2007, the Tenth Doctor confronted the Empress of the Racnoss in her lair beneath the Thames Flood Barrier. During the confrontation, he blew up the base, flooding the whole thing.

Donna watched as the Empress' Webstar took revenge on London, but it was quickly shot down.

Private Harris later reported that the Doctor had managed to stop the creature - "some sort of red spider", but that he had died in the process. (TV: Turn Left)

Behind the scenes
The script for Turn Left leaves it unclear as to whether the Empress of the Racnoss drowned beneath the Thames in Donna's World, or whether she was killed aboard the Webstar similar to her alternate self.