An ancient peoples of central Mexico from 1200 to 400 BC, probably the earliest people in the region. They resided mainly in Veracruz, Tabasco and along the coast of the Gulf of Mexico. They had a written language, math, and calendars.  Some indication of their practicing human sacrifice has been inferred.
The exact timeline and extent of this culture is still being explored. A group of expert findings and near-current understanding are found at 
Olmec or Maya
For many years the Maya were thought to be the "mother culture" of Mexico. But further examination of existing artifacts, combined with radiocarbon dating, show the Olmec to have been active in the region hundreds of years earlier.