The Vedas do not mention monkey people (vanaras), but the Mahabharata and the Ramayana do. The Vedas were composed 800-1000 years before these two epics. So the invention of the vanaras probably happened later, perhaps due to influence from indigenous religious ideas or perhaps a new set of myths. Interestingly, the Ramayana only gives vanaras monkey-like features but doesn't identify them as such, so there is some ambiguity about how they are to be represented.