C is for... CAL

When the Doctor and Donna Noble found themselves in the Library - a planet-wide repository for every known book ever published - they found that its computerised operating system was called CAL. They were joined soon after by an archaeological expedition led by Professor River Song. She was being financed by Strackman Lux, a descendant of the Library's creator. They had come to find out why the Library shut down 100 years before. CAL claimed that everyone present was saved, but there was no sign of anyone. The complex had become infested by Vashta Nerada - carnivorous microscopic creatures which live in darkness and mimic shadow. They prefer forest environments, but their trees were turned into paper and hence into books, which carried their spores.
Events in the Library were being witnessed on her TV by a young girl, also called Cal. She lived on Earth with her father, and was frequently visited by a physician - Dr Moon. She saw the Library as her own personal space, and was upset that there were intruders there. Dr Moon attempted to reassure her. Her actions influenced events in the Library.
Lux revealed that CAL stood for Charlotte Abigail Lux - his ancestor. She died as a child, but her father was able to save her consciousness into the data core of the Library, so that she would live on forever in every book stored there. A diagnostic program was set up to look after CAL on the nearby moon. The little girl was the consciousness of Charlotte, and Dr Moon her diagnostic program.
When she saved the people from the Vashta Nerada, it was electronically - downloaded into the data core. Everyone lived there in an artificial reality, looked after by Dr Moon. This included Donna for a time, where she had a husband and two children.

The Doctor made a deal with the Vashta Nerada to allow the saved people to go free and leave, whilst River Song sacrificed herself to prevent CAL from destroying itself. The Doctor was able to save River's consciousness to the core as well. She lived on with some of her colleagues, looking after Charlotte and Donna's children, whilst the planet was put into quarantine and left for the Vashta Nerada.

Played by: Eve Newton. Appearances: Silence in the Library / Forest of the Dead (2008).