From The TimeSplitters Wiki

The game's default star value for a bot is the Default AI. Default AI determines the intelligence, stamina, accuracy, agility and overall difficulty of defeating a bot. The Default AI is measure on a star scale of 1 to 5. For example, a 1-star bot will be slow to react to being shot and will die fairly quickly. In contrast, a 5-star bot is difficult to shoot at from behind due to their quick reaction time, and they will often perform dives and other dodges to avoid fire. 5-star bots have a large amount of stamina and will often run to retrieve a health pack when near death. Default AI values can only be changed when Character Abilities, are turned off.

Default AI does not apply to TS1 characters. When filling out a TS1 character's infobox, use "N/A."