Mendel was a monk and high school teacher whose work (he spent a decade hybridizing pea plants in the monastery garden) was published in small regional sources and languished in obscurity for decades. Nobody at the time understood the importance of his work, and biologists continued under mistaken models of how inheritance worked. Decades later other botanists did similar experiments, and then stumbled over Mendel's papers, and credited him for first developing and experimentally validating the correct model. e.g. Correns http://www.esp.org/foundations/genetics/classical/holdings/c...

As far as I know Mendel's model was much simpler and more clearly defined than anything that came before.