With a milestone homer that further cemented his legacy in South Korean baseball, slugger Lee Seung-yuop on Wednesday entered rarefied air that no one has reached, and no one likely will for quite some time.

The 38-year-old star for the Samsung Lions belted his 400thcareer home run off Koo Seung-min of the Lotte Giants at Pohang Baseball Stadium.

It's the alternate home for the Lions, who are based in Daegu, west of Pohang.

Lee became the KBO's career leader in home runs two years ago, hitting homer No. 352 on June 20, 2013, to surpass Yang Joon-hyuk's previous record.

With every ball that leaves the yard, Lee is rewriting the league record books.

Lee spent eight seasons in Japan's Nippon Professional Baseball (NPB) starting in 2004. He left the KBO at the peak of his power, immediately after establishing the new single-season record with 56 home runs at age 27.

That 2003 season capped off a string of seven consecutive years with at least 30 home runs, an impressive run that has never since been matched.

Lee averaged 43 home runs per season during that stretch, which included two 50-homer seasons.

If Lee had kept pace for a few more seasons in the KBO, it's conceivable that he'd have reached 600 by now.

Lee hit 159 homers in his eight-year NPB career, and the total could have been higher if not for his battles with injuries.

Lee virtually owns all KBO home run records that matter.

He is the youngest to reach career homer Nos. 100, 200 and 300. He was 26 years, 10 months and four days old when he connected for his 300th homer in 2003, younger than anyone either in Major League Baseball (MLB) or NPB.

As it stands, Lee, who turns 39 in August, is unlikely to reach 500 -- a sacred plateau in baseball -- but his home-run mark will still be safe for a while.

The next six players on the career home run list are all retired.

Lee Ho-joon of the NC Dinos is No. 2 on the active list with 299. He's 39 years old.

Only four other active players have hit more than 200.

Two hitters in their late 20s, Choi Jeong of the SK Wyverns and Park Byung-ho of the Nexen Heroes, each have 173 and 172 homers, but they too are unlikely to threaten Lee's record.

Choi isn't a prototypical slugger and he has never hit more than 28 homers a season.

Park has led the KBO in homers in each of the past three seasons and belted a career-high 52 last season.

Yet he is a late bloomer who didn't start playing regularly until late 2011, and he is eligible to be posted for interested MLB clubs after this season.

Lee was actually drafted as a left-handed pitcher out of high school.

After Lee suffered an elbow injury, his coaches recommended he consider switching to a position player.

It was a decision that didn't just change Lee's career -- it forever altered the course of South Korean baseball history. (Yonhap)