League of Legends is a Multiplayer Online Battle Arena (MOBA) game. Developed by Riot Games aka rito game. This is the most popular game in the world with a massive community of over 100 million players that you could meet at any large gaming event in the world. Riot Games has an enormous budget which allows them to create amazing cinematics, music, art, and animations frequently.
The third video above has a detailed explanation of gameplay.
Professional players join teams and come together from across the world to participate in tournaments with big prizes, these are often streamed on websites like Twitch where they gather a large audience.
(Esports)
At gaming conventions you can almost definitely find League of Legends players, sometimes in cool costumes. The community has it's own gaming sub-culture with things like these.
League of Legends features a roster of over 140 unique champions.