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.

Biography
Diagoras 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.

The Cult took Diagoras and Sec planned to merge with him. Daleks Jast and Thay protested, but Sec convinced them that polluting the Daleks' purity was necessary. 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.

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

Personality
Dalek Caan noted that Diagoras thought like a Dalek. Diagoras was an ambitious man and was generally cold and compassionless towards others. He also had a short temper, frequently snapping at anyone who questioned his orders.

Despite his seemingly cold nature, it is interesting to note that Dalek Sec gained human emotions after merging with Diagoras, which included mercy and compassion. This indicates that Diagoras may not have been as cold and aggressive as he appeared and might not have had as much in common with the Daleks as Caan had thought. (Although Sec felt Ambition, Hatred, Aggression, and love of war, so it's possible despite his emotions of mercy and compassion, he still has his Dalek-like personality.)