Mordred

Mordred, King Arthur's stunted son and nephew, (look it up, it's kind of a long story) is infamous for killing his father and breaking apart the renowned Round Table. Mordred was actually reported to be a very sweet child, until his mother Morgause gave him a Ring that turned him invisible, but also nursed his evil side. It was this Ring that inspired his treacherous ways, which were only stopped when Gawaine chased him into the mountains after finding him stroking the Ring and saying, in your Ingrateful Quote of the Day, "My...Precious..."