What group most directly influenced both the Maya and the Aztec?

The Olmec civilization most directly influenced both the Maya and the Aztec. As one of the earliest Mesoamerican cultures, the Olmec established foundational practices in art, architecture, and religious beliefs that were adopted and adapted by later cultures. Their developments in writing, calendar systems, and urban planning set the stage for the complex societies that followed, including the Maya and the Aztec.