EF-MD1991 was created years before Sonic Unleashed and was one of the first Egg Fighters ever created. In his service, EF-MD1991 worked diligently for Dr. Eggman, though his extensive work would wear down his AI.
When Eggmanland was created, EF-MD1991 was assigned to construct several passages inside it (despite finding this strange). Once finished, EF-MD1991 and the workers were overjoyed. EF-MD1991 was at some point told to watch out for Sonic the Hedgehog, but he forgot to see the arrest warrant and Sonic's image. EF-MD1991 was later awoken by Sonic and Chip, whom he thought were workers. Nervous, EF-MD1991 assured them that he was not goofing off and would talk with Sonic about how he would arrest him and the construction of Eggmanland (which he thought Sonic should check out), all while failing to realize who Sonic was. Tired of looking at him, EF-MD1991 then re-entered sleep mode.
EF-MD1991's work ethic and loyalty to Dr. Eggman are unequalled among the doctor's servants. However, his many years of service have worn down his AI, making him senile, slow, and prone to entering sleep-mode.
- The "MD1991" in EF-MD1991's name is a reference to Sonic the Hedgehog, which was released for the Sega Mega Drive in 1991.
- EF-MD1991's bio incorrectly states that he is the shopkeeper, a duty endowed to EF-DC1998.