Player Ally

A player ally is an NPC or a bot that will help the player, by providing covering fire if the ally has its own weapon. Allies can also be used to open special locked doors, with keypads If scripted so.

The difference between an ally and a Player Companion is that a companion is normally a long term helper, Examples include Alyx and Barney. Allies accompany you temporarily. Examples include: Citizens, Refugees, and Rebels.

A rebel is a good example ally, because his/her goal is to attack anything that they decide is an enemy. Use the point entity ai_relationship to change what it likes and dislikes.

The only main way that this branch of AI specificaly differs from others, is that it automatically Likes the player, though this can be changed with the aforementioned ai_relationship.