Sendol is a strong Korean 5d amateur player. He has been offered a 6d certificate, and he once aspired to become a pro. He is a professional baduk teacher in Seoul. His best ex-students are Hong Jangsik, Korean 7P, and Kim Taehyang, Korean 1P.
On KGS, he plays and teaches under various nicks. As Sendol, he is a KGS teacher. He puts a lot of pressure on reading - and asks his students to learn foremostly life&death, various tesujis - but also other aspects like fuseki, josekis etc. His own knowledge of josekis seems to be endless.
If you want contact him, see his info on KGS.
GGima 4d has dedicated the B2 Bomber strategy to him for he taught her many lessons in Go and life.