From The TimeSplitters Wiki

Khallos is Harry Tipper's archnemesis and is based of how a genric spy movie villain would look. Khallos has appeared in both TS2 and TSFP as Harry's rival.

TS2 Role

In Timesplitters 2, Khallos was the main villain in the Atomsmasher level. He set a laser on Harry Tipper, activated the bases self destruct, and ran off. Harry escaped and started disabling the bombs with the help of Dr. Peabody and his girlfriend Kitten Celeste. After the bombs were deactivated, Tipper grapped the time crystal and left, but Khallos got a hold of Kitten Celeste.

He also owns the Arcade level Hangar.

TSFP Role

Crow is now helping Khallos out, since they both are working towards a goal that will be much easier accomplished together. Cortez and Tipper infiltrate the base, but find out Khallos escaped on a train. After boarding the train and fighting their way through many henchman, the find Khallos, who activates a posion chamber with the two trapped inside. KHallos also reveals Kitten Celeste is on the track ahead, and flies off in his chair. Near the end of the level, the player fights Khallos and disables the train and save Kitten.

Strudel

Read about Strudel at his page.