Gregor Mendel is the Augustinian Monk and Scientist who developed the model of genetics that held sway all the way through the Darwinian Synthesis (when, essentially, it was introduced and integrated) and right up until recently, when it has weakened considerably compared to other conceptions of genetics based on observations not possible in his time. "Mendelian Genetics" still "works" more or less, it just applies to fewer cases in its original simple form. Mendel's main contribution was probably to demonstrate that inheritance involves both parents in roughly equal ways ant that the unit of inheritance is bot particulate and immutable between generations, so that even if a trait is invisible in an individual, the genetic material was not necessarily absent and could contribute to future generations. That (assuming "immutable" is not perfect) is all still pretty much both true and important. Read the comments on this post...