Fukui, Kenichi (1918-1998), a Japanese theoretical and experimental chemist, developed theories of how atoms join together in chemical reactions. He shared the 1981 Nobel Prize in chemistry with Roald Hoffmann, a Polish-born American chemist who worked independently in the same field. Fukui did much experimental work in organic chemistry.

In 1952, Fukui discovered that he could understand chemical reactions in terms of the density of the electron clouds around the reacting atoms. Electrons are the negatively charged particles that form the outer regions of all atoms. According to quantum theory, an electron cannot be regarded as having a precise location or following a precise orbit inside the atom. Instead, electrons must be viewed as swarming around the nucleus in clouds, called orbitals. It is the interaction between the electron clouds of neighboring atoms that cause atoms to bond together. Calculating exactly how atomic bonding happens is immensely complicated. Fukui found that a good guide as to whether particular atoms would combine to form a particular compound was to consider the densities of the electron clouds in the atoms. The highest-energy electrons of one atom (generally those in the outermost orbitals) would tend to be transferred to the other atom, forming a new orbital called a frontier orbital. From 1970, Fukui and his group of theoreticians extended his insight to the understanding of the course of chemical reactions and to the shapes of molecules.

Kenichi Fukui was born in Nara, Japan. He studied chemistry at Kyoto University and, in 1951, became a professor there. He lectured and taught there for 39 years. Fukui was dean of the faculty of engineering at Kyoto Imperial University, president of the Chemical Society of Japan, and director of the Institute for Fundamental Chemistry. He married Tomoe Horie in 1947.

They had two children.