From this LAT article:
Santa Muerte is not a Catholic saint, and in recent decades her popularity in Mexico, especially among the poor and criminal classes, has led to clashes with church officials and government authorities. Her first adherents included Mexican prisoners, drug dealers and prostitutes, and those in legitimate but dangerous nighttime work, such as security guards and taxi drivers.
"It's sort of like the Virgin for people on the edge," said Patrick A. Polk, a folklorist and curator at UCLA's Fowler Museum.
But in and around Los Angeles, where Santa Muerte services are held in at least three storefront shrines, a dash of pop theology and Southern California sunshine seems to have given the movement a mild New Age flavor.
Followers, many of whom call themselves Catholics, talk less about death than about cleansing the spirit and developing inner strength.