Inquisitor

Inquisitor was an office held by a member of the High Council of Time Lords. During the Sixth Doctor's trial on the Space Station Zenobia, Darkel assumed the role of Inquisitor, acting, in the terms of the British legal system, in the role of judge in order to evaluate his guilt or innocence. (DW: The Trial of a Time Lord)

There were a number of Inquisitors on Gallifrey. They served as judges and heads of inquiries. Darkel was Inquisitor Prime and appeared to be the senior Inquisitor and a member of the High Council. Darkel claimed that as Inquisitor General, he was the highest legal authority on Gallifrey. (BFG: Gallifrey)