The early Mortal Kombat games were monumental for a lot of reasons. They led to the creation of the ESRB rating system, popularized gore in fighting games, created an iconic competitive arcade game and spawned an incredibly successful franchise. An often-overlooked innovation of the first three Mortal Kombat games is that it helped popularize secret characters in fighting games. While MK wasn't the first series to have secret characters, it certainly has some of the more well-known examples.
Noob Saibot, Jade, Reptile and Smoke all got their start in the franchise as secret characters that were cryptically hinted at through in-game dialogue and context clues. While Reptile holds the distinction of being the first secret character in a Mortal Kombat game, there are few hidden kombatants quite as iconic as Ermac. While Ermac's story within the current Mortal Kombat timeline might be fairly well-known to fans, the story behind his addition to the series is legendary within gaming.
Rumors surrounding a secret character in the original Mortal Kombat's arcade release would be the catalyst for Ermac's creation. In the third revision of Mortal Kombat, a curious line of text reading "Ermacs" was added to the game's debug screen. Ermacs stood for "error macros" and was a way for the game to keep track of and catch any possible script errors that might occur. This term wasn't used outside of Midway, so it wouldn't exactly be expected for the average arcade player to know what this meant.
Speculation began to arise surrounding a possible second secret character in Mortal Kombat. The game already had Reptile, who players could fight in a special encounter if very specific conditions were met. The connection between Ermac and Reptile was only furthered by the error macro counter on the debug screen was located directly below the number of times the player had encountered Reptile.
Once fans began speculating, many took to the arcade to try and figure out how to unlock this mysterious hidden fighter. The only problem was that Ermac wasn't actually real, at least at this point. It was just a misconception brought on by an unknown term being added to the game's debug screen. Some people claim that certain versions of Mortal Kombat had a glitch where the name Ermac would replace their fighter's health-bar name, but this was proven to be impossible given how the game's code treated text.
The Ermac rumors only spread further when the magazine Electronic Gaming Monthly published a story from a reader who claimed to have encountered Ermac. The story also included an image that the reader has supposedly taken, which would show a red ninja and the text "Ermac Wins." While the image was actually just an edited photo of Scorpian, this EGM story is the earliest known instance of Ermac being dressed in red.
Even after Mortal Kombat II was released, Midway Games kept the rumors going by never giving a straight answer on whether or not Ermac was in the sequel. While a hidden message reading, "Ermac does not exist." could be found, series creators Ed Boon and John Tobias always kept answers regarding Ermac's existence very cryptic. While Ermac had fully gone from a rumor whispered in arcades to a gaming urban legend, he still wasn't an official Mortal Kombat character.
This would change with the release of Ultimate Mortal Kombat 3, as Ermac would finally become a canon kombatant in the MK universe. In a 2012 interview with The Gameological Society, Ed Boon explains that the development team wanted to make the urban legend of Ermac real. In a lot of ways, Ermac began as a fan-created character that was willed into existence through speculation and rumors. Even his color palette was technically created by a fan of the series through the EGM hoax.
While Ermac may not be Mortal Kombat's first or only secret character, he does have the distinction of being a fan-made fighter that has gone on to be featured extensively throughout the series. Since Ultimate Mortal Kombat 3, Ermac has appeared in eleven different MK games and has been playable in all but two of those. He's by far one of the most iconic ninja characters in the series and without a doubt one of the most important secret characters of all time.