An image consisting of a dog's head against a psychedelic background, with text above and below it. Spawned a number of imitators, most notably Courage Wolf.
Advice Dog was also used as bait during one of the 4chan.js attacks in 2008, and this theoretically should've led to him no longer being a meme. However, /b/ chose to overlook this. The lone positive contribution Advice Dog made was early in 2009, when a Anonymous chose to fight an Advice Dog thread by reviving Blockatiel, leading to much lulz from Advice Dog detractors.