Sombra is well known in Overwatch even though she isn't revealed yet. The reason why she is already well known is because Blizzard placed lots of easter eggs and hints on their maps about her. Sombra was the very first name we found in the Overwatch world.

The following text is just speculation. This might be true or false, we won't know until Sombra gets revealed.

¿Quién es 'Sombra'?

Sombra's first appearance was in a newspaper article found in Dorado. This article had the headline ¿Quién es 'Sombra'? which can be translated to "Who is Sombra?". Next to this there was a photo of a shadowy figure. The next hint was found on a table. There were three files with the names Jack Morrison, Soldier: 76 and Sombra. Jack Morrison is well known as the former commander of Overwatch and Soldier: 76 is a hero in the game. There were also two photos of them next to the files. The name Sombra appeared again on some of the security screens in Dorado. Sombra seems to have a connection to Soldier: 76 and also seems to be more than a computer virus.

Newspaper found on Dorado

Animated Short: Hero

In the Animated Short video Hero you can see Soldier: 76 fighting against some bad guys who want to rob a little girl. Those guys were called Los Muertos and want to rule the city by fear. Soldier: 76 decided to fight against them and destroy their plans. In this video we see that Dorado was in trouble and was not safe. We still don't know anything about Soldier: 76's plans in Dorado or if he completed his mission but we know that he saved a little girl named Alejandra.

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Overwatch Animated Short, who is this girl?!

When Soldier: 76 saved Alejandra she asked him if he is one of the heroes she has seen on the posters on the street. He replied: "Not anymore". So why is this video named "Hero" when Soldier: 76 refused to be a hero? A simple answer to this would be that this video is not actually about Soldier: 76. There wasn't something like a background story of him in this video like the other Animated Short videos had for their characters. Instead it showed us the background story of Alejandra. This would perfectly fit into the other Animated Short videos where we always see something like a background story of the characters. This would be Alejandra's background story. So far we have no hero named Alejandra in the game, so she has to be a new one. Alejandra's hometown is Dorado and the map where we first found clues about Sombra was also Dorado. So it could be possible that this Animated Short was actually about Sombra's story. Sombra is of course grown up now because the Dorado we saw in the video was not like the Dorado we know from the game right now. In the Animated Short the big nuclear plant wasn't built yet and this means there was a lot of time between the Animated Short and the current version of Dorado.

Dorado

Let's take a closer look at Sombra's hometown. Dorado is a city which was ruled by a gang named Los Muertos. You can still find their spray in the current Overwatch map. Right now it seems like they disappeared from the city. However other big things happened to Dorado. LumériCo planed to build one of their nuclear plants in Dorado. It is now known as the destination of the payload in the current version of the Overwatch map. LumériCo built those nuclear plants all across Mexico to provide clean energy for the whole country. We know that Sombra has something to do with LumériCo, because it seems like she hacked herself into their system.

Found in the Dorado nuclear plant

We also know that Soldier: 76 made some attacks against financial institutions and that he was in Dorado. So maybe he tried to attack LumériCo. If this theory is true, then maybe Alejandra decided to be a hero like Soldier: 76 and she decided to help him. This would explain why Sombra hacked the nuclear plant in Dorado.

The Shadow

We found out that Sombra has something to do with Dorado and we also know that the newspaper article was not related to the picture of Ana. So this shadow from the newspaper still exists. Sombra is translated to "Shadow", which would perfectly fit into the whole Dorado theme. A big organisation built a power plant and some bad gang members rule the streets. It seems like there is a huge gap in the society of Dorado and that Sombra tries to be a hero for her people. Because of some leaked voice lines we also know that Sombra is a she. Reaper says "Where is Sombra when we need her?" when he is in a team with Soldier: 76. This means that Soldier: 76 knows who Sombra is. With this theory Sombra almost has to be Alejandra, the little girl Soldier: 76 saved in Dorado.

Alejandra, from Animated Short: Hero

Conclusion

I know that there are many speculations about Sombra. Some people think that she is an Omnic and is related to hacking and stealth. This could be true since her name is translated to "Shadow" and she appears on the security system. But I think that her origin is Dorado, where we found the first clue about her. Also the theory about the Animated Short video sounds pretty accurate to me. Soldier: 76 was a rolemodel for the young Alejandra so she decided to be like him and help him to fight against the bad guys. Keep in mind that all this is speculation and maybe nothing is correct from this.