Mara Salvatrucha (MS-13) is a criminal (“terrorist”, now) organization out of California. It was initially made up of Salvadoran teenagers that escaped the country during civil war back in the 80s, as they banded together forming street gangs to fight and protect themselves from the larger LA gangs that would extort migrants. Over time the gang evolved into a full criminal organization while expanding to activities like international trafficking, kidnapping and murder.

If you want to know more, reading history of Ernesto Deras is a good place to start.