Riot Games, Inc. is an American video game developer, publisher, and esports tournament organizer based in Los Angeles. It was founded in September 2006 by Brandon Beck and Marc Merrill to develop League of Legends and went on to develop several spin-off games and the unrelated first-person shooter game Valorant. In 2011, Riot Games was acquired by Chinese conglomerate Tencent. Its publishing arm, Riot Forge, oversaw the production of League of Legends spin-offs by other developers until its shutdown in January 2024. The company worked with Fortiche to release Arcane, a television series based on the League of Legends universe.

Riot Games operates League of Legends esports leagues and the Valorant Champions Tour. The company, which had 23 offices worldwide as of 2023, sells corporate sponsorships, merchandise, and streaming rights for its leagues. Riot has faced allegations and lawsuits alleging a toxic workplace culture, including gender discrimination and sexual harassment. The company was criticized for its use of forced arbitration in response to these allegations.

Brandon "Ryze" Beck and Marc "Tryndamere" Merrill, the founders of Riot Games, became friends while roommates at the University of Southern California, where the two studied business. Beck and Merrill believed too many video game developers diverted their focus from game to game too often, distinguishing Defense of the Ancients as an indication that games could be supported and monetized long-term. They also drew inspiration from Asian video game designers who released their games for no up-front cost, and instead charged for additional perks.

Beck and Merrill sought funding from family and angel investors, raising US$1.5 million to launch their company. Riot Games was established in September 2006 in Santa Monica, California. The first person Riot Games recruited was Steve "Guinsoo" Feak, one of the early developers of DotA Allstars, a game considered to have been foundational to the MOBA genre. As they refined League of Legends' initial creation, they pitched investors a video game company rooted in e-commerce. Merrill said that they approached publishers who were baffled by the game's lack of a single-player mode and free-to-play business model. Riot Games received several rounds of funding totaling $8 million, including investments by the Benchmark and FirstMark Capital venture capital firms, as well as Chinese holding company Tencent. The latter would later become League of Legends' distributor in China, and then the parent company of Riot Games.

Following six months of beta tests, Riot Games released League of Legends as a free-to-play game on October 27, 2009. Their game designers and executives participated in online forums to make adjustments based on player feedback. On May 10, 2010, Riot Games announced that they would take over distribution and operation of their game in Europe; to do so, Riot Games relocated their European headquarters in Brighton to new offices in Dublin. In February 2011, Tencent invested $400 million for a 93 percent stake in Riot Games. Tencent bought the remaining 7 percent on December 16, 2015; the price was not disclosed.

In 2012, in response to toxicity and harassment in League of Legends, Riot Games launched a "player behavior team" of psychologists to combat harassment on its platform. Riot Games' tactics to address issues on League of Legends, which included an opt-in chat function between opposing players, informing banned players of the reasoning behind the ban, as well as creating a tribunal of players to weigh in on bans, resulted in a 30 percent drop in reported harassment behavior. The efficacy of their results has been questioned by players and the gaming press. By 2013, League of Legends was the most-played multiplayer PC game in the world. By 2016, Inc. reported the game had over 100 million monthly players.

Riot Games relocated to a new building on a 20-acre (8-hectare) campus in western Los Angeles in 2015. In March 2016, Riot Games acquired Radiant Entertainment, another developer who was working on Rising Thunder and Stonehearth at the time. Rising Thunder was effectively canceled following the acquisition, with the game's team allocated to a new project. On October 13, 2017, Beck and Merrill announced that they were returning their focus to developing games, aiming to create new experiences for video game and esports players. Beck and Merrill handed over the day-to-day operations and overall management of the League of Legends team to three longtime employees: Dylan Jadeja, Scott Gelb, and Nicolo Laurent, who previously served as chief financial officer (CFO), chief technology officer (CTO) and president, respectively. Subsequently, Gelb and Laurent assumed roles as chief operating officer (COO) and chief executive officer (CEO), respectively, while Beck and Merrill became the Riot Games' chairmen. As of May 2018^[update], Riot Games employed 2,500 people, operating 24 offices around the world.

In October 2019, Riot Games announced several new games: a version of League of Legends for mobile devices and consoles called League of Legends: Wild Rift, a standalone mobile version of the Teamfight Tactics mode from League of Legends, and the digital collectible card game titled Legends of Runeterra, with all three scheduled for a 2020 release. The company also teased further games — Project A, a tactical shooter; Project L, a fighting game with League of Legends characters; and Project F, a multiplayer game set in Runeterra – that were not detailed outside of genre descriptions and brief gameplay clips. Project A was later revealed to be Valorant, which entered closed beta on April 7, 2020 and was officially released on June 2, 2020.