No, there is no secret 24th character in Mortal Kombat 1
Despite countless rumors and speculations suggesting that Mortal Kombat 1 has a secret 24th character, the final starting roster actually consists of ...

Despite countless rumors and speculations suggesting that Mortal Kombat 1 has a secret 24th character, the final starting roster actually consists of only 23 characters.
As is always the case with fighting games, Mortal Kombat fans have been discussing the most about which fighters will make it into the starting roster and how many of them there will be since the first revelation of MK1 earlier this year. Over the past few months, there have been countless leaks of the lineup (most of which turned out to be false), but now that the game has finally been released, we can finally confirm how many fighters there are.
Thanks to the launch trailers released earlier this week, we already knew 23 of the playable characters in the lineup. Unfortunately, I can confirm that contrary to some fan speculations, there is no 24th character that can be unlocked by completing the story or invasion mode. The final version of the game actually includes 23 playable fighters.
This means that NetherRealm Studios made an unusual decision to reveal all playable characters in the initial version of Mortal Kombat 1. This is particularly interesting when considering that Mortal Kombat 11 had a secret character in the form of Frost, who was unlocked after completing the story and was only revealed after the game's launch, similar to Mortal Kombat 9 with Cyber Sub-Zero.
Mortal Kombat 1 actually rewards you with a fighter when you complete the main story, but it is a character that we already knew was present in the game - Havik. It is not clear why he is hidden behind the campaign compared to the other fighters, but if you want to play as the Chaosrealm's troublemaker, you have to complete the game first.
The story is the same with the cameo fighters, as NetherRealm has also revealed all of them. Some of them, like Scorpion, Sub-Zero, and Shujinko, are unlocked by progressing in the game and upgrading their profile, but there is no fighter that will be a surprise for those who have followed the marketing of Mortal Kombat 1.
Much of the confusion about a possible 24th character seems to stem from leaked images of the character select screen that surfaced in recent weeks. These leaked images showed a grayed-out slot for a 24th character, which many hoped would be filled either by completing the story mode or downloading the day-one patch.
However, that is not the case, as this grayed-out slot is actually the area where the DLC characters will be added, as indicated by the clearly visible large plus sign on the image.