There is no formal definition of what makes a companion but it typically refers to a character who travels with, and shares the adventures of the Doctor. Companions have assumed a variety of roles in Doctor Who, as involuntary passengers, as assistants, as disciples, as friends, and as fellow adventurers.
First Doctor
* Susan Foreman
* Ian Chesterton
* Barbara Wright
* Vicki Pallister
* Steven Taylor
* Katarina
* Sara Kingdom
* Dodo Chaplet
* Polly Wright
* Ben Jackson
Second Doctor
* Polly Wright
* Ben Jackson
* Jamie McCrimmon
* Victoria Waterfield
* Zoe Heriot
Third Doctor
* Brigadier Lethbridge-Stewart
* Liz Shaw
* Sergeant Benton
* Jo Grant
* Mike Yates
* Sarah Jane Smith
Fourth Doctor
* Sarah Jane Smith
* Harry Sullivan
* Leela
* K-9 Mark I
* K-9 Mark II
* Romana I
* Romana II
* Adric
* Nyssa
* Tegan Jovanka
Fifth Doctor
* Adric
* Nyssa
* Tegan Jovanka
* Vislor Turlough
* Kamelion
* Peri Brown
Sixth Doctor
* Peri Brown
* Jamie McCrimmon
* Melanie Bush
Seventh Doctor
* Melanie Bush
* Dorothy "Ace" McShane
[edit] Eighth Doctor
* Grace Holloway
Ninth Doctor
* Rose Tyler
* Adam Mitchell
* Jack Harkness
Tenth Doctor
* Rose Tyler (Actor Billie Piper)
* Mickey Smith
* Donna Noble (Actor Catherine Tate)
* Martha Jones (Actor Freema Agyeman)
* Jack Harkness
* Sarah Jane Smith
* River Song
* Astrid Peth
* Christina de Souza
* Adelaide Brooke
* Wilfred Mott
Eleventh Doctor
* Amelia Pond (Actor Karen Gillan)
* River Song
* Rory Williams
