The Summoner is a term commonly used to describe a League of Legends player, and it is used to track statistics and scores for each player. It is also, in lore, a person who primarily uses summoning magic for battle.
Ancient battles between Protectorate (Stag crest) and Magelords (Owl crest) summoners waged on the field known as Summoner's Rift. Helped by a mysterious figure, the war between both sides has changed the landscape and mutated the local flora and fauna. Now a the battlefield is littered with the ruins of both sides and is a residence of a powerful Dragon and Baron Nashor.
A player in League of Legends takes on the role of a summoner, a gifted spell caster who has the power to bring forth a champion to fight as their avatar in the Fields of Justice. With all major political decisions on Valoran now decided by the outcome of the contests that take place in the battle arenas, a summoner is the key force of change on the continent. As the summoner controls the champion in combat, the summoner also influences the outcome of the match through the use of summoner spells, runes, and masteries. Once a match is over, the summoner gains experience and influence points. Experience points allow the summoner to gain increased powers by unlocking additional spells and rune slots, while influence points allow the summoner to gain access to new champions and new runes for use in future fights.
(As of late 2014, Riot has stated that the concept of a Summoner (as found in the lore of the game) is to be altered, Institute of War is gonna be removed and thus the in-lore League of Legends is to be "Fully Relaunched" again.)
The Summoner's Code is a list of rules and guidelines that Riot Games provides to the players to abide to when participating in competitive play. If a summoner disobeys this code they might find themselves suspended for an amount of time. Repeated and/or severe infractions will incur harsher penalties. Any player can report a summoner that has disobeyed the code in a match; if this summoner gets reported a sufficient number of times, his actions will be reviewed by other summoners in the Tribunal.
The Summoner profile page is the players personal page, which is accessible and part of the PVP.net interface. Its primary use is to track the players game statistics, to showcase game achievements and players champions roster. It also has several customizable esthetics features to better visually distinguish a player amidst other League of Legends players (for example: profile banners, frames, and summoner icons), and bonus pre-game customizable features which use is to enhance players champion stats and also to to add different bonus abilities before each match. These bonuses fall into three categories: summoner spells, runes, and masteries.
Summoners are allowed the use of any two of the summoner spells during any battle in the Fields of Justice, many are available from the start while others are unlocked through gaining levels. These spells are controlled by the left hand and significantly impact gameplay. There is one specific mastery in Preseason 4 that lowers the cooldown of summoner spells, which is Summoner's Insight
Before a battle arena match begins, a summoner can make use of Runes to enhance their champion's abilities. Runes can only be purchased with Influence Points at the Riot Store.
Runes may not be bought with Riot Points. This is to help prevent people from buying power, although you can acquire runes faster by buying an Influence Points Boost.
Masteries are perks that affect gameplay, they are commonly referred to in other games as "skill-trees". All of the masteries are passive effects although some augment summoner spells, which can be activated. A summoner is able to focus their intense magical training into specific categories (Offensive, Defensive, and Utility). Each group has 6 tiers, within a group all but the first tier are locked when you first start, with a successive tier opening with each 4 points spent in the same group. Lines in the mastery tree imply additional unlocking criteria. The summoner can put one point per level (up to level 30) into masteries. Masteries can be re-distributed at will between battles. Since May 23, 2011, summoners are allowed to have multiple saved mastery pages.