Yinchuehshan was originally the user name of a NEXON technician who was tasked to perform maintenance on NEXON INC. servers in 1999. The character was little different than a Delphi character, and was used for the same reasons.
Yinchuehshan was later used as a Delphi character by the GM Eldridge, but somewhere along the line Yinchuehshan was turned into an event character for events which occured during patch upgrades to the NexusTK client, the most famous of which was the Yin's Gift Event and Yin's Postcard Event.
Largely because Yinchuehshan was perceived as a benevolent entity by the players, Yinchuehshan was also used by GM Eldridge to hold Q&A sessions where players could ask questions and Yinchuehshan would broadcast the answers which many players would accept was undeniable truth because they mistakenly believed Yinchuehshan was not the same person as GM Eldridge; therefore since Yinchuehshan was purported to not be a NEXON INC. employee, players believed he had no reason to lie.
Since many within the NexusTK community held negative opinions about the GM Eldridge, Yinchuehshan was used as part of a "Good cop, Bad cop" strategy. Whereas GM Eldridge would punish players, Yinchuehshan would appear to bring gifts (such as new features, events and client patches).
It should be noted that it is rather amusing how many players truely believed Yinchuehshan was actually being sent from South Korea to the United States in order to help NEXON INC. install server patches when all of this tech support work is actually done through a network.