The hostess was a human who served the beings who wanted to go to the planet Midnight, via shuttle bus.

When the ship was attacked by the Midnight entity, it possessed Sky Silvestry. The hostess was the first person to consider whether they should throw Sky out. After she realised that Sky was still possessed and had stolen the Tenth Doctor's voice, she gave her life to defeat Sky by throwing herself and Sky out the shuttle door.

After her death, the Doctor asked the surviving passengers, "The hostess, what was her name?" None of them had any idea. (TV: Midnight)

The Doctor later remembered her, during the 21st century Dalek invasion, when Davros asked him about the many people who had died for him. (TV: Journey's End)