Why Every Classic Companion Left Doctor Who
15. Katy Manning - Jo Grant
Katy Manning became Doctor Who's longest serving female companion - up to that point - when she played Jo Grant opposite Jon Pertwee's Third Doctor for three whole years. The introduction of Jo Grant, and the paternalistic relationship between her and the Doctor solidified the UNIT family dynamic that would lend more warmth and levity to the rest of the Pertwee era.
Katy Manning made the decision to leave to pursue other acting work at the end of Doctor Who season 10. Manning's departure was the beginning of the end for the UNIT family, which began to wind down the following year.
Manning returned for the show's modern era, with appearances in The Sarah Jane Adventures and The Power of the Doctor respectively.