Spyder
From Guild of Archivists
Spyder was a fictional OOC character, created at Cyan around Riven's release. Spyder released clues concerning how to find the easter eggs in Riven and, later, realMyst. The true identity of Spyder, or whether Spyder is represented by one individual at all, rather than multiple Cyan employees, has never been revealed.
The tradition of releasing information about an upcoming game through online riddles has been continued with several of the Myst games after Riven, and is something many fans enjoy solving together.