|Place of origin:||Earth|
|Appearances:||Daleks in Manhattan, Evolution of the Daleks|
|Main actor:||Eric Loren|
Mr Diagoras was an American businessman who oversaw the construction of the Empire State Building. He was also secretly a servant of the Cult of Skaro, and ran the work to fit the orders of Dalek Caan, who served as the Cult's connection to the outside world.
The Cult thought Diagoras was the most Dalek-like human they had encountered, as he had rare ambition and thought like a Dalek. Dalek Sec viewed Diagoras as their best option for the Final Experiment, so Caan took him to meet their leader.
Deep within the Cult's subterranean lair, Dalek Sec revealed to Diagoras that he planned to merge with him. Daleks Jast and Thay protested, but Sec convinced them that polluting the Daleks' purity was necessary, as the Daleks must survive. Sec opened his casing and Diagoras was pushed into his Dalek-mutant flesh. Sec fully encased his body in him, and the casing was closed. When the Final Experiment was complete, the casing opened and Sec stepped out, transformed with Diagoras into the first human-Dalek.
It is unclear whether Diagoras was still living when he was merged with Sec or if his mind was aware of his surroundings.
Diagoras was an ambitious man, and was generally cold, uncaring and ruthless towards others. He also had a short temper, frequently snapping at anyone who questioned his orders. His personality on the whole was very similar to that of a Dalek — a fact that did not go unobserved by Dalek Caan.
Despite Diagoras' seemingly cold nature, Dalek Sec gained human emotions after merging with Diagoras, which included mercy and compassion.