The Catalogue of Life was created by Light as a list of all organic matter.
The catalogue of life was the work of centuries. When Light went to sleep, life started to evolve. Light was angered as this evolution had made the catalogue invalid as it did not contain any knowledge of many species that now dominated the Earth, including humans. Light decided to kill humans instead of simply re-recording the new species. The Seventh Doctor showed Light that life would always evolve, so Light gave up on the catalogue and dispersed. (TV: Ghost Light)