Riley Vashtee

Riley Vashtee was a crew member aboard the S.S. Pentallian under Commander Kath McDonnell.

Biogrpahy
The Pentallian was mining from the sentient star Torajii. Shortly after Martha Jones arrived onboard with the Tenth Doctor in the TARDIS he developed a strong attraction to her. While trapped in an escape pod and thinking they would both soon die in the fires of the star, Martha reciprocated Riley's sentiments in what they thought was their last minutes together.

The Doctor having rescued them, though, Martha kissed him on the lips before she departed in the TARDIS with the Doctor, leaving Riley to his life on the S.S. Pentallian. (DW: 42)

Several months before the incident, Vashtee first met Erina Lessak in a coffee house Erina's family owned on Torajii Alpha. Physically attracted to Vashtee, Lessak befriended him and afterwards decided to join the crew of the Pentallian as a trainee engineer. (WC: 42 Prologue)

Behind the scenes

 * Dialogue in the episode, combined with references on the Doctor Who website, implies the character is bisexual.