Yoshio Koide (小出 義夫, Koide Yoshio; born May 16, 1942, in Kanazawa, Ishikawa) is a Japanese theoretical physicist specializing in particle physics. He is best known for the Koide formula, a relation among the masses of charged leptons that has attracted attention for its surprising accuracy. While some physicists regard the formula as potentially significant, others consider it to be a numerical coincidence.
Source: “Yoshio Koide”, English Wikipedia (CC BY-SA 4.0), excerpt