Diagoras

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.

Diagoras' choice of attire was somewhat gothic — he wore black shoes, slacks, shirt, and a tie — even his hair was black. He also fought in World War I, and it was then that he decided to only take care of himself. He also developed an ambition to run New York City, whatever it took.

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.

What was left of Diagoras, merged with Sec, was exterminated by Dalek Thay. (TV: Daleks in Manhattan, Evolution of the Daleks)

Personality
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, although when the foreman argued with him over the work on the mast, Diagoras kept his cool and was vague over telling the foreman who his masters were.

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.