Which protagonist was known by the least amount of people?
It seems that Jin Yong's protagonists were all pretty well known (except maybe Wei Xiaobao), but not so for Gu Long's. For example, Ye Kai was all but forgotten within a few years of his story. It seems that he didn't make a name for himself at all, but Fu Hongxue was more well known.
For Jin Yong, I'd say Duan Yu, Xu Zhu, and Shi Potian were low profile, while Guo Jing, Yang Guo, Zhang Wuji, Chen Jialuo, Xiao Feng were high profile. Not sure about Linghu Chong.