Eye of C'Thun is the proof of the Old God C'Thun's defeat.
The Eye of C'Thun begins a short chain quest:
You get to choose one of the following at the end of the quest chain:
Eye of C'Thun is also the name of C'Thun's gigantic eyeball form in phase 1. However, the item is described as "an eye stalk of the fiend", which is likely the eye of a tentacle.
Patches and hotfixesEdit
Patch 1.9.0 (03-Jan-2006): Added