Gregor Mendel

... was born Johann Mendel, in 1822, in the village of Heinzendorf bei Odrau. The village was then in the Austrian Empire, but is now in the Czech Republic (known as Hynčice). Mendel's family had farmed in Heinzendorf for well over 100 years. From 1840 to 1843 he studied practical and theoretical philosophy and physics at the Philosophical Institute of the University of Olomouc, in Moravia – now the second oldest university in the Czech Republic. He joined the Augustinian friars at St. Thomas's Abbey in Brno (known in German as Brünn) on the suggestion of his physics tutor, because it helped to pay for his education; this is when he took the name Gregor.

He was encouraged by his professors at Olomouc, and also by his colleagues at the monastery, to study variations in plants. He studied seven traits that seemed to be inherited independently of others (including seed shape, flower colour, and height). He discovered that when different varieties were crossed to each other (for example, when tall plants were fertilised by short plants), one in four pea plants had purebred recessive traits, two out of four were hybrids, and one out of four were purebred dominant. His experiments led him to make two generalisations: the Law of Segregation (that every individual organism contains two alleles for each trait, and these alleles separate during meiosis such that each gamete contains only one of the alleles) and the Law of Independent Assortment (that alleles for separate traits are passed independently of one another, i.e. from parents to offspring). These later came to be known as Mendel's Laws of Inheritance.

(An allele is a variant form of a given gene. Meiosis is a specialised type of cell division, as opposed to mitosis which is the normal form. A gamete is a mature sexual reproductive cell, which unites with another cell to form a new organism.)

Mendel became Abbot of the monastery in 1867, after which his scientific work effectively came to an end. He died in Brno in 1884, aged 61.

Wikipedia explicitly gives Mendel's nationality as Austrian. The Austro–Hungarian Empire came about in 1867 when the Kingdom of Hungary was established as a separate state, no longer subject to Austrian rule.