Companion is a term used to refer to the Doctor’s friends who usually accompany him in his travels and adventures. The companion can be picked up from all around time and space to travel with the Doctor. They often provide the Doctor with a different perspective, aiding him in his exploits and even saving his life sometimes. On occasion, the Doctor has sacrificed himself, regenerating, in order to save a companion; though the inverse has happened before, with the companion dying in their effort to help the Doctor. A companion can stay with the Doctor for varying lengths of time, some staying with him even through a regeneration.