Professional Gaming Career

Season 3

Lee was picked up by SK Telecom T1 K in 2013 as their starting mid laner. SKT T1 K dominated the Korean scene, and in October 2013, Lee led them to win their first League of Legends World Championship. Later in the HOT6iX Champions Summer 2013, Lee cemented his status as a brilliant player due to his perfect Zed outplay against KT Rolster Bullets mid laner Yoo "Ryu" Sang-wook, which would then become one of the most iconic moments in League of Legends history.

Season 4

In 2014, SK Telecom T1 K followed their success through in the OGN winter season, making the entire run without dropping a single game. They would then go on to win All-Star Paris 2014. However, their Winter season success did not follow through and during the Spring and Summer seasons, SKT T1 K failed to qualify for the 2014 World Championship. In the following offseason, Riot Games changed the team regulations so that each organizations may only have one team participating in each league. This led to the merger of SKT T1 K and SKT T1 S, and the subsequent departures of Impact and Piglet for the NA LCS. The new team would compete under the name SKT T1.

Season 5

After the 2014 season, Lee reportedly declined an offer of over $1,000,000 by a Chinese team, preferring to stay in Korea on SKT. In November 2014 it was reported that Lee had declined contract offers from several Chinese companies including one offer of ₩500 million ($425,403 USD) for streaming. Throughout 2015, Lee shared the mid lane position with Lee "Easyhoon" Ji-hoon. Depending on the team composition SKT wanted to play, either one of the players could be substituted into the game. Lee had many notable performances in the LCK such as a pentakill against NaJin e-mFire with his LeBlanc. SKT ended the summer split in first place and advanced to the world championship. At the 2015 World Championship, Lee and his team won while only dropping one game in the finals for a record of 15–1 throughout the tournament.

Season 6

Lee and his team started off the 2016 Season by winning the LCK Spring Split. With this victory, SKT was guaranteed a spot in the 2016 Mid-Season Invitational. At that point in time, MSI was the only major international tournament they had yet to win. They were heavily favored coming into the tournament, but were initially unable to perform up to their usual standards, unexpectedly losing several games in the group stage. However, they managed to turn things around during the elimination round and eventually clinched the title by sweeping the North American team, Counter Logic Gaming, in the finals. On July 11, 2016, Lee became the first player to reach 1,000 kills in the LCK. His 1,000th kill was on MVP Beyond's Reksai, which he achieved on Malzahar. SKT placed third in the 2016 LCK Summer Split, but still qualified for the 2016 World Championship through circuit points. The team swept through the group stage and advanced towards the playoff round. In the semifinals they defeated the ROX Tigers in a close 3–2 series. In the finals they defeated Samsung Galaxy in another close 3–2 series, winning their third world championship title. Lee was voted as the Most Valuable Player of the tournament.

Season 7

Lee renewed his contract with SKT with an "unprecedented offer", which was rumored to be over $2.5 million USD. On February 6, 2017, Lee recorded his first live stream on Twitch and had a peak viewership of 245,100, setting a record at the time for the most views for a single streamer in the history of the site. However, this record was broken in early 2018 by another League of Legends streamer named Tyler1. Lee and his team later won the 2017 LCK Spring Split, clean sweeping KT Rolster 3–0 in the finals. This win qualified them for the 2017 Mid-Season Invitational. At the 2017 Mid-Season Invitational, SKT topped the group stage with a 8–2 record. SKT swept Flash Wolves 3–0 in the semifinals and defeated G2 Esports 3–1 in the finals to become the first team to win the Mid-Season Invitational back to back. At the 2017 World Championship, SKT were still considered by many to be strong favorites to lift the cup for a third consecutive time despite not winning the LCK Summer Split. After a 5–1 group stage, SKT narrowly defeated Misfits and Royal Never Give Up in the quarterfinals and semifinals respectively, before facing Samsung Galaxy in a repeat of the previous year's final. Despite being favorites going into the game, SKT were swept 3–0 by SSG, ending the SKT domination at the World Championship. Lee himself was shown to be visibly upset after the loss, and had to be consoled by his teammates to shake the Samsung Galaxy players' hands post-game. However, this caught the attention of many League of Legends fans throughout the world, with much support and many tributes being given to the team's legacy and Lee for his continued success.

Season 8

Lee played his 400th match in the LCK on July 17, 2018. They successfully defeated their opponent, MVP, 2–1. SKT finished fourth in the 2018 Korea Regional Finals, failing to qualify for the 2018 World Championship.

Season 9

On November 20, 2018, it was announced that Lee had re-signed with SKT for another three years. He had been listed on Forbes 30 Under 30 Asia 2019, under the category of Entertainment & Sports. On April 13, 2019, SKT won the 2019 LCK Spring final, earning Lee his seventh LCK title. In May 2019, SKT represented the LCK at the 2019 Mid-Season Invitational. They finished the group stage in second place but lost 2–3 to G2 Esports in the semifinals. On July 7, 2019, SKT, along with three other LCK teams, won their league's first Rift Rivals championship title after defeating LPL teams by 3–1. After winning his first Rift Rivals title, Lee became the first and only player to have won all of the League of Legends international tournaments (Mid-Season Invitational, World Championship, Rift Rivals, All-Star) organized by Riot Games. Lee played his 500th match in the LCK on August 21, 2019, during the LCK Summer Playoffs. He won his 500th game against Afreeca Freecs with Qiyana, with a KDA of 7/1/14. He won his eighth LCK title along with his team members on August 31, 2019 in the 2019 Summer LCK Final. His team qualified as the LCK's first seed for the 2019 League of Legends World Championship. On October 27, 2019, Lee achieved his 100th international win after defeating Splyce at the 2019 World Championship. At the 2019 World Championship, SKT was once again defeated by G2 Esports in a semifinals series, losing 1–3.

Season 10

On February 18, 2020, T1 announced that Lee had re-signed with them for three years, in which his contract will last until the year 2022. He also became a part owner of T1 Entertainment and Sports. On March 5, 2020, Lee became the first player to have reached 2,000 kills in the LCK. The champion used when achieving his 2,000th kill was Zoe. On April 25, 2020, Lee claimed his ninth LCK title after he and his team defeated Gen.G at the 2020 LCK Spring finals.

Season 11

On February 3, 2021, Lee played his 600th game in the LCK. He is the first to achieve the 600 game mark in the LCK. His 600th game was against NS RedForce, which he locked in Orianna and achieved a KDA of 2/0/6. He won the game, and was awarded as the MVP of the game. This was also his 399th win in the LCK. On February 6, 2021, Lee became the first player to achieve 400th win in the LCK. His 400th win was against Fredit Brion, and the champion picked was Sett. During the 2021 League of Legends World Championship, Lee was eliminated in the Semifinals in a 3-2 victory in a best-of-5 series against DWG KIA. His team qualified as the 3rd seed from the LCK via the LCK Regional Qualifier. His team had an overall record of 5-1 in their Group Stage, and 5-2 in the Brackets/Knockout Stage of the tournament. His team beat teams such as Edward Gaming, 100 Thieves and Hanwha Life Esports throughout the tournament to get to Semifinals. On November 19, 2021, T1 announced that they had re-signed with Lee.

Season 12

On February 18, 2022, Lee played his 1,000th career game against KT Rolster. He was the second player to achieve the milestone. He locked in Leblanc and won the game. On February 20, 2022, Lee played his 700th LCK game. He is the first to achieve the 700 game mark in the LCK. The game was against NS RedForce in which he locked in Ahri for the game. During the 2022 LCK Spring Split, Lee was a member of the team that went undefeated in the regular season with an 18-0 record, becoming the first team to achieve this record since the league’s inception. In the playoffs, Lee achieved his 10th LCK title, defeating Gen.G in the finals 3–1. On July 8, 2022, Lee became the first player to achieve 500 wins in the LCK. The match was against Gen.G.