Martha was also intended to make guest appearances in the 2009 series of Torchwood and The Sarah Jane Adventures, but could not due to the actress's other work commitments.

[1] Within the series' narrative, Martha begins as a medical student who becomes the Doctor's time travelling companion after an incident at the hospital where she works.

After returning to life on Earth, becoming engaged and finishing her medical degree, Martha finds a newfound level of independence when she is recruited into the paranormal military organisations UNIT and, briefly, Torchwood.

Freema Agyeman's first appearance in Doctor Who was in the second series (2006) episode, "Army of Ghosts", where she played Adeola Oshodi, Martha's cousin.

When the hospital she works at is teleported to the Moon, medical student Martha helps save the day alongside an alien time traveller known only as the Doctor (David Tennant).

Able to remember the events during the Master's reign, Martha then leaves the TARDIS of her own accord, telling the Doctor that she cannot waste her life pining for someone when the relationship cannot happen, but promises that she will see him again.

[7] Martha, as voiced by Freema Agyeman, also appears in the 2007 animated serial The Infinite Quest, which aired in twelve weekly segments during the run of the 2007 series.

First appearing in the episode "Reset" as part of a three-episode story arc, Martha has been temporarily drafted to the Torchwood organisation of alien-hunters by Jack, requiring a medical expert on alien life.

Through exposition, it is revealed that Martha has become a "medical officer" for the international paranormal investigations agency UNIT since qualifying as a Doctor of Medicine.

Martha returns again for the final two episodes of the series, "The Stolen Earth" and "Journey's End", where she has been promoted to a U.S. division of UNIT and is working on a top-secret teleportation project based on Sontaran technology.

She rallies alongside fellow companions Jack and Sarah Jane Smith (Elisabeth Sladen) in an effort to face the threat of Davros' (Julian Bleach) plot to destroy reality.

[9][10] In facing Davros, Martha threatens to set off nuclear warheads which will destroy the Earth in order to spare human suffering and curtail his plans, but is stopped by the Doctor.

A scene in "The End of Time" (2010) shows Martha, apparently having left UNIT, fighting aliens with Mickey and marrying him rather than her previous fiancé.

[28] As with her predecessor Rose, Martha is from London; Brett Mills from the University of East Anglia presumes this is because characters from the capital of the country are "therefore relatable to all British people" because they are seen as "neutral".

[31] In casting Martha, the actress Freema Agyeman was reused from her minor role as Adeola Oshodi, in the Series 2 episode "Army of Ghosts".

[32][33] Appearing in Torchwood, it is explained through exposition that Martha is a medical specialist for UNIT,[34] a qualified doctor and bona fide expert on alien life.

[34] First appearing on the spin-off series in Torchwood episode "Reset", fellow companion Jack Harkness establishes Martha's credibility to her new peers, slyly commenting upon her vast experience.

In "The Poison Sky", she cites her relationship with Thomas Milligan as a reason to stay on Earth, rather than join Donna and Doctor in the TARDIS — saying that she's now got a great big adventure of her own to enjoy.

[36] Director Euros Lyn comments that the production team had intended for Agyeman and Clarke to join Torchwood for its third series, but their careers led them elsewhere.

[12] Head writer and executive producer Russell T Davies explains that Agyeman was cast in Law & Order: UK before Children of Earth had been officially commissioned.

In response, Davies created the character of Lois Habiba, played by Cush Jumbo, to be a "kind of a Martha figure", one with added innocence who is out of her depth.

[41] In some instances, Martha's status as a middle-class woman distinguishes her from earlier black companion Mickey Smith, who is male and, like Rose Tyler, working-class.

[43] Lindy A. Orthia opines that such Tenth Doctor era representations of "Earth's past as a place of happy and benign diversity" may be anti-racist in intention, but ultimately trivialise the racism that she claims has "infested" Western society for centuries.

In "Human Nature", in addition to the racist jibes of private school boys, "we bear witness to how things have changed, when a white nurse refuses to believe that Martha is a medical student in the future, saying, "Women might train to be doctors, but hardly a skivvy and hardly one of your colour.

"[40] When the TARDIS crew are nationally branded as terrorists in "The Sound of Drums", the Master (Simm) says that the Doctor's current companions "tick every demographic box" – referring to Martha's gender and ethnicity and Jack's sexual orientation.

Episodes set in the future, Orthia notes, are more often than not inclusive and "cosmopolitan" projections of societies which are as multi-racial (though not multi-ethnic) and sexually liberal as the present, if not more so.

"[H]owever fantastic and 'unreal' the experiences of Martha and Lisa might be, their characters are always situated within a set of family relationships that most viewers would recognise as being fairly commonplace."