Lee "kurO" Seo-haeng joined his first professional team when Incredible Miracle 2 was formed in March of 2013. The team played in the first OGN at HOT6iX Champions Summer 2013 where they couldn't make it to the quarterfinals and placed last in their group.
The next OGN they attended was PANDORA.TV Champions Winter 2013-2014 where they failed to make it past the group stage again. Their streak of poor performances continued at HOT6iX Champions Spring 2014 where they failed to make it through groups for a third consecutive time. Shortly after the tournament ended, kurO departed from the team to join NaJin Black Sword. He played his first OGN with the team at HOT6iX Champions Summer 2014 where they made it to the quarterfinals but lost 3-2 to SK Telecom T1 S.
On October 31st 2014, it was announced that kurO had parted ways with NaJin Black Sword. On November 14th, 2014, kurO joined the newly formed HUYA Tigers together with Smeb, Lee, PraY, and GorillA. The team played in the Champions Spring 2015 Qualifiers along with Incredible Miracle, Prime Clan, and Xenics, where they finished 2-1 and qualified for Champions Spring 2015. The team then renamed to GE Tigers. GE started out unarguably the top team in Korea at SBENU Champions Spring 2015 and earned themselves an invitation to the IEM Season IX World Championship in March. However, after defeating Cloud9 and SK Gaming to win their group, they lost 2-1 to Team WE in the semifinals. This defeat was considered by many casters and analysts to be the biggest upset to date in the entire history of League of Legends competition. They qualified for the finals of the OGN playoffs because of their first place finish in the regular season. Unfortunately, they lost 3-0 to SK Telecom T1 in the finals and placed second. The team renamed to the KOO Tigers prior to the start of SBENU Champions Summer 2015. KOO placed fourth in the regular season and qualified for the playoffs but lost 3-2 in the semifinals to KT Rolster. Because SKT won the finals, KOO still qualified for the 2015 Season World Championship as the second seed due to circuit points. KOO was placed into a group at worlds with Counter Logic Gaming, Flash Wolves, and paiN Gaming. They placed second, ending with a 4-2 record. They beat KT Rolster 3-1 and Fnatic 3-0 to make it to the finals against SKT. However, they finally fell in the finals with a 3-1 loss.
Soon after Worlds, Koo dropped the team as a sponsor and they renamed to the Tigers. The Tigers played in the 2015 LoL KeSPA Cup but they were upset in the first round 2-0 by SBENU Sonicboom. The Tigers renamed to ROX Tigers in January.
During the 2016 LCK Spring Split, the ROX Tigers dominated domestically in similar fashion to 2015. They finished the regular season with a 16-2 match record, losing only to KT Rolster and Samsung Galaxy. Earning first place in the regular season gave them a bye to the finals of the Spring Playoffs, where they faced SK Telecom T1. ROX entered as the favorites this time, but still lost 3-1, earning themselves second place for the spring split.
During the 2016 LCK Summer Split, the Tigers once again placed first in the regular season with an impressive 15-3 scoreline in Bo3s, with two losses to SK Telecom T1 and one loss to Samsung Galaxy. This seeded them in the 2016 LCK Summer Playoffs directly into their third domestic finals, where they eventually met KT Rolster. In an epic series, the ROX Tigers won the set 3-2, claiming 1st place in the Summer Split and giving them Korea's first seed into the 2016 Season World Championship.
At the 2016 Season World Championship, the ROX Tigers were placed into Group A, along with G2 Esports, Counter Logic Gaming, and Albus NoX Luna.