This review gives a detailed description of the life path of the founder of genetics, Gregor Mendel, who forever entered the pleiad of the most significant personalities in the history of mankind with his peas experiments. Now all biologists know the "Mendel's laws" and the famous trait inheritance a ratio of 3:1. The development of modern DNA sequencing technologies allowed to identify genes of the four of the seven divergent traits studied by Mendel and their localization on chromosomes. The remaining three traits may be encoded by several genes and it is unclear what Mendel used to control specific phenotypes. Unfortunately, the other objects chosen by Mendel and, in particular, the hawkweeds showed the opposite result to the peas due to the apomictic reproduction. Mendel's laws cannot apply to them in principle, but at his time no one knew this yet. In addition, Mendel's introduction of mathematics into biology was so revolutionary that it was misunderstood by his colleagues. Only one scientist, our fellow countryman I.F. Schmalhausen, saw the importance of the results obtained by Mendel, mentioning his 1866 article in the dissertation in 1874. He noted that the method of presenting botanical results in the form of formulas deserves further development. It took more than three decades before the rediscovery of Mendel's laws, accomplished in 1900 almost simultaneously and independently by three scientists - G. de Vries, K. Correns and E. Cermak. Reasoning about certain material carriers, Mendel, in fact, predicted the existence of units of heredity in the form of genes. He demonstrated the binary nature of inherited traits, providing evidence of the sufficiency of one pollen grain for fertilization of an egg. On the basis of experiments with dioecious plants he put forward a hypothesis about the genetic determination of sex. But Mendel's main merit is that his pioneering work gave a very powerful impetus to the further development of this area of research. His works are significant not only for the plant science, since the laws he discovered are applicable to all sexually reproducing organisms. Since Mendel's working notes have not been preserved, and very few articles have been published by him, many of his achievements, including breakthrough ones, are known from the letters he sent to the botanist K. Nageli. In these letters he outlined the results of his research on crossing various plants, but Nageli didn’t pay much attention to the results, focusing only on the hawkweeds. On the bicentennial anniversary of Mendel's birth, his complete genome was sequenced. Bioinformatic analysis of his genome made it possible to discover pathogenic variants of genes that could lead to some diseases, including those manifested in his youth. This review also pays attention to the formation of Mendel as a scientist and the period of his life when he was still Johann.
