Mara Salvatrucha, commonly known as MS-13, is an international criminal gang that originated in Los Angeles, California, in the 1970s and 1980s. Originally, the gang was set up to protect Salvadoran immigrants from other gangs in the Los Angeles area. Over time, the gang grew into a more traditional criminal organization. MS-13 is defined by its cruelty, and its rivalry with the 18th Street gang.