The background pony that everypony should know. She does the most random things you can ever think of. She is the new and better version of Where's Waldo, at least in season 2. In season 1 episode 1 she was seen in the background when Twilight Sparkle was pouring " hot sauce " into her cup. She was spotted randomly and now she became a known background character. Most famous from her googley eyes and her randomness.
Derpy has gained a huge following by the fandom known as "bronies". She gained popularity due to an intentional animation joke. Originally, her face was supposed to be covered up, but a last minute change to the layout of the background revealed her, and Thiessen did not order her eyes fixed, as the episode had already been approved to air by the Hub. After her face was spotted by a sharp-eyed user of the /co/ board of 4chan, who also gave her her name, her popularity took off.