In the Dream of the Red Chamber, Cao Xueqin's encyclopaedic novel, Zhen Shi-yin is a seemingly minor character that appears in the first and last chapters of the book, and is never directly connected to any of the main protagonists.
Thr fact that the first few chapters of the novel are a kind of false start before the actual plot, such as it is, starts, is one of the many things that make this novel somewhat hard to approach. However, when viewed on the symbolic level, Mr. Zhen is an important part of the novel.
Zhen Shi-yin is a scholar living in somewhat gentile poverty. Despite his hard times, he helps Jia Yu-cun become a government official, but Zhen later loses his money, his daughter is kidnapped, and after having to deal with some rude relatives, he leaves the world to run off with a Mad Taoist. But before he does, he has a dream where the previous reincarnations of the main characters in the book in the fairy realm are explained.
Zhen's connections to the major characters of the book, the Jia Clan, are two fold. First, his student, Jia Yu-cun uses his alleged connection to the Jia family to gain his powers. Secondly, his kidnapped daughter, not knowing her background, is adopted by the Jia family as a maid, named Caltrop.
Figurativly, Zhen is connected to the Jia family because Zhen is a pun on "real" and Jia is a pun on "false". Thus, the entire story is figurativly a lie, with only the fleeting presence of the awakened Zhen at the beginning and end to give it reality.
Zhen Shi-yin also gives the concluding speech in the last chapter of the book, explaining how the entire book is just an illusion, but an illusion that the protagonists did indeed learn from.