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Most of the animal breeding theory we are still using today, was invented in the first half of the 20-th century. The statistician R. A. Fisher (1890 – 1962) showed that the diversity of expression of a trait could depend on the involvement of a large number of so-called Mendelian factors (genes). He published a lot related to statistics and animal breeding, but his keynote paper came out in 1918. Fisher, together with Sewall Wright (1889 – 1988) and J.B.S. Haldane, were the founders of theoretical population genetics. Thomas Hunt Morgan (1866-1945) and co-workers connected the chromosome theory of inheritance to the work by Mendel and created a theory where chromosomes of cells were believed to carry the actual hereditary material. Morgan won the Nobel prize for it in 1933.In the first half of the 20^th century Iowa State University in Ames, Iowa, USA was the place to be. It was home to Jay L. Lush (1896 – 1982), who is known as the modern father of animal breeding. He advocated that instead of subjective appearance, animal breeding should be based on a combination of quantitative statistics and genetic information. His book 'Animal Breeding Plans' that was published in 1937 greatly influenced animal breeding around the world. Lanoy Nelson Hazel (1911-1992) was inspired by Lush's book and started working for him, also in Ames. He received his PhD degree in 1941 and in that PhD thesis he developed the selection index theory, a method used for decades to determine what weights should be put on the different traits under selection. In the process of developing this method he also came up with a concept on how to estimate genetic correlations. This is essential for assigning the proper weight to selection traits. Hazel also developed a method using least squares, a statistical technique, for more complicated data with unequal numbers of subclasses as often occur in animal data. Until then, statistical techniques by Hazel were used to optimise weighing the performances for various traits in animals to select those with the most optimal combination. The estimated breeding value (ebv) was only developed later by the statistician C. R. Henderson (1911 – 1989), who was a student of Hazel in Ames. The estimated breeding value made it possible to rank the animals according to their estimated genetic potential (the ebv), which resulted in more accurate selection results and thus a faster genetic improvement across generations. Henderson further improved the accuracy of the estimated breeding value by deriving the best linear unbiased prediction (BLUP) of the ebv in 1950, but the term was only used since 1960. He also suggested to integrate the full pedigree of the population to include genetic relationships between individuals. This way performance of relatives could be included in estimating the breeding value of an individual. The so-called animal model was born. Unfortunately in those days the computer power was too limited to be able to also calculate the breeding values using the animal model. The practical implementation thus had to wait until the later 1980's. Current great minds that have developed a way to incorporate large scale DNA information that has become available in animal model (BLUP) theory to estimate the so-called genomic breeding values are Theo Meuwissen (currently professor in Ås, Norway) and Mike Goddard (currently emeritus professor in Melbourne, Australia).