From The TimeSplitters Wiki

Brown Zombie
Unlocked by	Challenge > 1-B Putrid Punchout
Species	Zombie
Size	Normal
Accuracy	N/A
Agility	N/A
Stamina	N/A
Fire Proof	N/A
Shock Proof	N/A
Default AI	N/A
Native TimeZone	1935-65
First Appearance	TS1 Story Mode
Relations	N/A
Games	TS1

Brown Zombie is a generic zombie, who doesn't look brown contrary to his name. Green Zombie shares his characteristics and appearence except he is inversely arranged (brown zombie's eye is on the left, green zombie's is on the right).He appears in the Tomb level halfway through

TS1 Gesture	Gets up from the ground whilst grunting.	TSFP Gesture	N/A
TS2 Gallery	N/A	TSFP Gallery	N/A