Quake Bots are computer-controlled players. Generally, they have very sophisticated AI (Artificial Intellect) to simulate a human player. A bot can be quite hard to defeat - don't think that if you can beat a monster you can beat a bot controlled by the same computer. Bots are made to kill - kill human players. Download one and take a shot yourself.

There are many bots and variations available at bots section of the Absolute Quake Files Archive directory at ftp.cdrom.com.

Name	Homepage	Description
Reaper, v0.81	Discontinued	Reaper bot is probably one of the most advanced (smart) bots out there. These bots can actually remember the layout of a level and where artifacts and weapons are. There are many variations available here.
Eliminator, v1.41	Official Page	Eliminator is another most advanced bot - they are fast and accurate. The only drawback of this model is that level must be specially pre-processed to include "navigation points" for the bot. There are many pre-processed maps and bot variations here.
Zeus, v2.042	Official Page	This is an excellent bot that can be used both as an assistan in single player games and an opponent in deathmatch.
CTF Bot v1.2	Official Page	This is a bot designed to play Capture The Flag.