From The TimeSplitters Wiki

TS Series

The games in the series all play a part in the TimeSplitters history. What TS really is about is a war between the Splitter and the Human race. The main character, Sgt. Cortez goes with his sidekick Corparl Hart to retrive ther Time Crystals stolen by the Splitters. The crystals hold the power to go back in time and the Splitters are using it to change the history of the Human race to thier intrest.