William Bateson is credited as being the first to use the word epistasis to describe the distortion of Mendelian ratios due to gene-gene interactions. A 2002 paper in the Journal of Genetics by Bateson (no direct relation) provides a short biography of William Bateson.
Bateson, P. William Bateson: a biologist ahead of his time. J Genet. 2002 Aug;81(2):49-58. [PubMed]
William Bateson coined the term genetics and, more than anybody else, championed the principles of heredity discovered by Gregor Mendel. Nevertheless, his reputation is soured by the positions he took about the discontinuities in inheritance that might precede formation of a new species and by his reluctance to accept, in its full-blooded form, the view of chromosomes as the controllers of individual development. Growing evidence suggests that both of these positions have been vindicated. New species are now thought to arise as the result of genetic interactions, chromosomal rearrangements, or both, that render hybrids less viable or sterile. Chromosomes are the sites of genes but genes move between chromosomes much more readily than had been previously believed and chromosomes are not causal in individual development. Development, like speciation, requires an understanding of the interactions between genes and the interplay between the individual and its environment.