L was in a project and each person involved where named a letter in the alphabet. I.e L and B.
B could never surpass L so he left wamies house and decided to work on his own and commit a series of murders and gamble weather he would be caught our not. It was all really to get back at L, and create a case that HE couldnt solve. Twords the end of the book, we find you that BB he was born with shenegami eyes, he doesn't have a death note, and a full life span.
anyway, niomy ends up catching him. You HAVE to read the book, there are so many important details!