Wikipedia
The were-jaguar was both an Olmec motif and a supernatural entity, perhaps a deity.
The were-jaguar motif is characterized by almond-shaped eyes, a downturned open mouth, and a cleft head. It appears widely in the Olmec archaeological record, and in many cases, under the principle of pars pro toto, the were-jaguar motif represents the were-jaguar supernatural. The were-jaguar supernatural incorporates the were-jaguar motif as well as other features, although various academics define the were-jaguar supernatural differently. The were-jaguar supernatural was once considered to be the primary deity of the Olmec culture but is now thought to be only one of many.
Originally, many scholars believed that the were-jaguar was tied to a myth concerning a copulation between a jaguar and a woman. Although this hypothesis is still recognized as viable by many researchers, other explanations for the were-jaguar motif have since been put forward, several questioning whether the motif actually represents a jaguar at all.
The term is derived from Old English were, meaning "man", and jaguar, a large member of the cat family in the Olmec heartland, on analogy with werewolf.