The term Bot in League of Legends refers to computer controlled opponent (AI - Artificial Intelligence) available in custom games and co-op vs. AI matches. Bots can have either "beginner" or "intermediate" AI.
On January 24, 2012 it was announced that the bot system would be expanded with more bots, better intelligence and availability on the Crystal Scar. On February 01, 2012, the system was released.
Bots can be used for:
Practicing against or learning how to play a new Champion;
Filling in for missing players to even out teams;
Leisurely play for those who do not want to experience such competition between summoners;
New players who want to familiarize themselves with the game (champions, maps, items, item builds, champion skills, strategies etc.) before competing with other summoners.
Runes and Masteries
Intermediate bots take 15 mastery points and have 16 runes--five each of Tier 2 Marks/Seals/Glyphs and one Tier 2 Quintessence. Intermediate bots have no increased stats except for a boost to their passive gold gain.
Beginner bots have neither runes nor masteries.
On January 24, 2012 it was announced that new bots would be added to the existing pool. This was implemented on February 01, 2012.
Since this update are 54 of 118 (45.76%) champions available as bots.
To add a bot into a practice game, you must first be the creator or the host of the game. Then, click the "Add Bot" button on the right of the empty slot to add a bot to the corresponding team. Once a bot has been added, you can then change the Champion of the bot by selecting it from the drop-down menu.
In the new tutorial, Battle Training, four new bots appeared, with a high AI, these are: Shen, who plays on the player's team, and Annie, Malphite, and Nasus, who opposed the player.
During Sona's release in patch V184.108.40.206, she was unintentionally added onto the bot roster. Bots' names are usually made up of the champion name followed by the word "Bot" (e.g. Annie Bot). However, Sona went by the name "game_bot_sona". She did nothing but autoattack and she was removed from the bot roster with V220.127.116.11. She has been reintroduced as a standard bot with the Rise of the Bot Army update.
After the update, Nasus and Alistar appear to be scheduled for removal as bots. However, it is possible that they will still be able to be selected in custom games, but won't be available in random player vs AI games. They, together with Malphite and Sivir, were unavailable in that mode before the update.