The artwork of Realm of the Mad God may seem familiar. The 8x8 sprites are from a Creative-Commons artwork set made by Oryx in 2009 called "LoFi Roguelike". Oryx gave permission for anyone to use this artwork for non-profit purposes, which was exactly what Wild Shadow Studios did when they started.
When Wild Shadow decided to make a business out of RotMG, they approached Oryx and negotiated the purchase of a license to keep using Oryx's artwork. Since then, Wild Shadow has made more art for use in their game, and plans to continue using this iconic style.