"Captain Jack Harkness" was the alias adopted by a Time Agent and con man from the 51st century who became an associate and occasional companion of the Doctor. He was made reluctantly immortal by the Bad Wolf entity and stranded on Earth from the mid-19th to the early 21st century. During much of that time, he worked for Torchwood Three until its destruction in 2009. He left Earth in 2010 and did some soul-searching. However, he returned to Earth in 2011 when Miracle Day spread across the world. Jack decided to stay on Earth afterwards and establish a new Torchwood team.
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| Companions of the Ninth Doctor (Medium with Fanon) | |
|---|---|
| Original to television | Rose Tyler • Adam Mitchell • Jack Harkness • Lynda Moss |
| Original to prose | Ali |
| Original to comics | Tara Mishra |
| Companions of the Tenth Doctor (Medium with Fanon) | |
|---|---|
| Original to television | Rose Tyler • Mickey Smith • Sarah Jane Smith • K9 Mark III • Jackie Tyler • Donna Noble • Martha Jones • Jack Harkness • River Song • Astrid Peth • Jenny • Rosita • Jackson Lake • Lady Christina de Souza • Cassie Rice • Jimmy Stalkingwolf • Adelaide Brooke • Wilfred Mott |
| Original to prose | Gisella • Alsa • Nikki Jupiter • Rok Ma • June • Koral • Jon Bowman • Jake and Vienna Carstairs • Wallace Fitch • Emily Parr • Kate Maguire • Christina de Souza 2.0 |
| Original to comics | Majenta Pryce • Maxwell Edison • Heather McCrimmon • Wolfie Ryter • Matthew Finnegan • Emily Winter • Gabby Gonzalez • Rose • K9 • Cindy Wu • Alistair Gordon Lethbridge-Stewart • Grayla |
| Original to audio | Sugar MacAuley |