Lee Jae Dong joined team Plus (???-Plus) in 2005, which in early 2006 (March 23) became Lecaf OZ.

He made his progamer’s debut on 13 February 2006 and his big stage debut in SKY Proleague 2006 Round 1, on the 30th of April. He achieved his first win in Proleague about a week later, against JiHyun (Hul at the time). Although 2006 was Jaedong’s first year in the professional StarCraft scene, he was already doing extremely well, having an overall record of 51 wins and 27 losses (65.4% win rate). This was the second best Zerg win rate of 2006, right behind sAviOr (GGPlay was third with 63.5%). His early wins against notable players included sAviOr, Reach, NaDa, GoRush, July, and iloveoov. It was clear early on in Jaedong’s career that his Zerg vs. Protoss and Zerg vs. Zerg were outstanding, being both above 70% (vs. Protoss 75% and vs. Zerg 71.4%). After the 2006 Season Lee Jae Dong was prized on 2nd Annual Korea e-Sports Awards with the Rookie of the Year Award.

It was Jaedong’s massive streak against Terran in mid-late 2007 that brought him into the mainstream spotlight. During this run he went 12–0 against Terran, which included scalps against NaDa and Hwasin. Jaedong’s rise during 2007 coincided with the demise of sAviOr. He finished off his brilliant 2007 by capturing his first Starleague title. Finally in January 2008 Jaedong captured the throne of No.1 Zerg according to the KeSPA Ranking, a title that he has held on for more than two years and a half, and still counting. After the 2007 Season Lee Jae Dong was prized on 3rd Annual Korea e-Sports Awards with the Best Winning Percentage, the Best Zerg, and the Player of the Year Awards. 2008 proved another successful for Jaedong claiming an MSL gold (technically in the 2007 Season) and a silver. He also managed to claim the No.1 overall KeSPA Rank for four straight months.

Later on in his career, Lee Jae Dong demonstrated that his monstrous Zerg vs. Zerg wasn’t just a chain of lucky games. Even though Jaedong was extremely successful at Zerg vs. Zerg in his early career, he later said that he didn’t feel confident at all playing it. However, his great success in televised games, especially in Zerg vs. Zerg, allowed him to get even better at it (see also). Soon, Zerg vs. Zerg became Jaedong’s trademark match-up with a winning rate of over 81% in the middle of 2009, allowing him to become the most successful Zerg vs. Zerg player in history. Indeed, Jaedong’s ZvZ mastery allowed him to reach the highest vs. Z ELO ranking ever recorded, edging out previous bonjwa and TvZ monster iloveoov. After the 2008–09 Season Lee Jae Dong was prized on 4th Annual Korea e-Sports Awards with the Best Zerg Award, and the Player of the Year Award.

After his win in the Bacchus Starleague 2009 and the resolution of the Free Agency Controversy (see below), Lee Jae Dong announced that he would undergo Lasik eye surgery to repair his rapidly deteriorating vision. His surgery is scheduled for September 28th. On 26 January 2009 Daily eSports announced: accepted to Seoul Cyber University School of Multimedia Design Lee Jae Dong will be a freshman in university this March. He applied for the regular admission which had its deadline on the last December 29. Overcoming a low admission rate, he received the acceptance letter.

Lee Jae Dong was the WCG 2009 champion and has won five major league titles: the EVER Starleague 2007, the 2008 GOMTV MSL Season 4, the Batoo Starleague, the Bacchus Starleague 2009, and the NATE MSL. Jaedong took out YellOw[ArnC] in the Bacchus Starleague 2009 in a 3–0 sweep, becoming the third Golden Mouse holder and the second progamer (after SlayerS_`BoxeR`) to win back-to-back Starleagues. In addition to his major league titles, Jaedong also won titles at the Seoul IESF 2007, the WCG 2008 Korea Championship, the WCG 2010 Korea Championship, and the TG-Intel Classic Season 1, a surprisingly one-sided series where he defeated Lee Yong Ho (Flash) 3–0 in the Final. He was No.1 overall KeSPA Rank from April 2009 till February 2010 (for eleven straight months).

2010 was the year defined by the rivalry between Jaedong and Flash. The two progamers faced each other in no less than 5 finals: WCG Korea, NATE MSL, 2010 Hana Daetoo Securities MSL, 2010 Bigfile MSL consecutively, and the Korean Air OSL 2. In these finals Flash came ahead 3-2, though Jaedong held a slight edge in their head-to-head record, an incredible feat considering Flash's domination at the time. Jaedong finished the year with a monstrous 70% win rate, behind only Flash, and yet again received the KeSPA Award for Best Zerg.

In 2011 Jaedong fell into a relative slump, with a win percentage lower than his rookie year (though he reached the round of four in the 2011 PDPop MSL and 2011 ABC Mart MSL). Peculiarly, his best matchup ZvZ and favored matchup ZvP fell to the 50% range, whereas his ZvT rose to an all-time high of 81.1% for the year (TLPD). After the disbandment of Hwaseung OZ, WeMade FOX, and MBCGame HERO, KeSPA formed an eighth team to allow the players of the former teams to continue to play. Though the Eighth Team has struggled in Proleague, Jaedong has remained their top-performing player.