Started out as a solo musician in 2002, he joined SG Wannabe in 2004. He went solo again in 2008, and became pretty famous in Japan too. I'm not entirely sure what his reputation is in the US.
I think he's an excellent musician, just not my cup of tea. Regardless, I give my condolence for the loss. During his last interview, he said that people only care about being number 1... on the chart, sale, and not care about humanity, quality of music, musicianship, etc. I suppose that might be what drove him to this.
Here's a popular song by Dongha Chae, Soon-a-bo (순애보)