Willi Hennig, German biologist and entomologist (d. 1976)
Emil Hans Willi Hennig (20 April 1913 – 5 November 1976) was a German biologist who is considered the founder of phylogenetic systematics, also known as cladistics. In 1945 as a prisoner of war, Hennig began work on his theory of cladistics, which he published in German in 1950, with a substantially revised English translation published in 1966. With his works on evolution and systematics he revolutionised the view of the natural order of beings. As a taxonomist, he specialised in dipterans (true flies).

Hennig coined the key terms synapomorphy, symplesiomorphy and paraphyly. He also asserted, in his "auxiliary principle", that "the presence of apomorphous characters in different species 'is always reason for suspecting kinship [i.e., that species belong to a monophyletic group], and that their origin by convergence should not be presumed a priori' (Hennig, 1953). This was based on the conviction that 'phylogenetic systematics would lose all ground on which it stands' if the presence of apomorphous characters in different species were considered first of all as convergences (or parallelisms), with proof to the contrary required in each case." This has been viewed as an application of the parsimony principle to the interpretation of characters, an important component of phylogenetic inference.He is also remembered for Hennig's progression rule in cladistics, which argues controversially that the most primitive species are found in the earliest, central part of a group's area.