These people were members of the hereditary nobility and occupied the top positions in the government, the army and the priesthood. Pipiltzin helped increase social stresses which attributed to internal weaknesses of the Aztec Empire's downfall.
As the Aztecs began settling what would later become their homelands, an elite emerged (the pipiltzin) that claimed descent from the Toltecs, the former empire of Central Mexico. The new hereditary elite unified the clans that had been the center of Aztec life and paved the way for a conquest empire.
This is also were the Pipil people of western El Salvador get their name, they are descendants of Toltec people who migrated and settle in El Salvador.