Season 8

As of 2017, season 8 remains notable for being the season with the most number of regular characters. Not only did it see a new companion in the form of Jo Grant, but it featured a regular enemy — The Master — who was the first regular Time Lord enemy of the Doctor to appear more than twice, and an expanded regular UNIT cast that now included Sergeant Benton and Mike Yates in most episodes. Adding in returning regulars Jon Pertwee and Nicholas Courtney, the regular cast swelled to six.