The Olmecs were the first Mesoamerican civilization, and while no other cultures that might have influenced it are known, this culture influenced the ones thace came after it, hence gaining the name "mother culture.
The Olmec beliefs are known to us thanks to archeological funds and comparison to other cultures. At the present moment 8 deities are assumed, but the work on understanding the Olmec culture is still ongoing. Those deities are: Olmec Dragon, Bird Monster, Rain Spirit, Maize deity, Banded-eye God, Fish Monster, Feathered Spirit and Jaguar.