The Cyber King was one of the largest monsters in recent Doctor Who and although somewhat primitive in design was very the less an incredibly powerful foe that towered over the cityscape.
One CyberKing was created by Cybus Cybermen in London in 1851. The Tenth Doctor theorised that the end of the 2009 Dalek Invasion of Earth collapsed the walls of the Void, allowing the Cybermen to escape and travel back in time using a stolen Dalek Dimension Vault. Using child labour to generate electricity and produce the ship underneath the River Thames, Mercy Hartigan was made into the CyberKing. She refused to be cyber-converted, and instead used her mental powers to command the entire Cyberman army. The ship rose out of the Thames, with Miss Hartigan and several Cybermen controlling the machine inside the part of the vehicle shaped as a Cyberman mouthpiece, and rampaged across London. Using Jackson Lake's " TARDIS" and an improvised device made from Cyber infostamps, the Doctor severed the link between Hartigan and the Cybermen. The Cybermen and Miss Hartigan were killed in the process, and the CyberKing was transported into the vortex.