The Chief Scientist was the leader of the Dalek Scientific Division. It was third in the Dalek Empire's chain of command, taking its orders only from whatever Dalek Supreme was currently acting as the Dalek Emperor's second-in-command.
The Chief Scientist reported to the Black Dalek that the Doctor's TARDIS had been located, allowing the latter to send a time-travelling execution squad of Pursuer-Daleks after the First Doctor and his companions. (PROSE: The Chase)
After the Golden Emperor's "perfection" was called into question during the Super-Skaro year, a group of Dalek Scientists, headed by the Chief Scientist, were tasked by the Emperor with taking him apart and rebuilding him with an increased brain capacity. After identifying the minor flaws in the Emperor's casing, the Scientists decided to rebuilt it completely, creating a much larger casing in Skaro's Great Hall with an enlarged, artificial organic brain to supplement the mutant, rather than a mere computer brain. The Chief Scientist, wearing a "special protective Dalekoat", was the one to finish plugging some cables connecting the casing to the wall. (COMIC: The Secret of the Emperor)
The Chief Scientist was part of the Kar-Charrat mission to obtain information from the planet's library. It was sent on that mission by an Dalek Supreme, immediate subordinate to the Dalek Emperor. The Chief Scientist and other Scientist Daleks created the first Dalek test subject. The first one went mad. The second test subject obtained the information, but it disobeyed the Dalek Supreme's orders. After he ordered the Supreme to self-destruct for his failure, the Emperor placed the Chief Scientist in command of the Dalek Supreme's mothership. (AUDIO: The Genocide Machine)