Companion

Companion was a somewhat vague term used to describe the Doctor's closest friends. Such people knew the Doctor's "secret": that they were someone non-human who travelled in time and space in a police box-shaped craft called the TARDIS. The Doctor's companions often directly saved the Doctor's lives or provided the Doctor with a perspective that prevented them from abusing their Time Lord powers. On some occasions, they were the proximate reason that the Doctor sacrificed their then-current life and regenerated. On others, they lost their lives in pursuit of the Doctor's goals.

Companions of the Doctor
This list is presented in chronological order from the Doctor's in-universe point of view. As such companions from projects produced several years after their placement on this list are included in such a way.