Motonori Matsuyama (松山 基範, Matsuyama Motonori; October 25, 1884 – January 27, 1958) was a Japanese geophysicist who was (in the late 1920s) the first to provide systematic evidence that the Earth's magnetic field had been reversed in the early Pleistocene and to suggest that long periods existed in the past in which the polarity was reversed. He remarked that the Earth's field had later changed to the present polarity. The era of reversed polarity preceding the current Brunhes Chron of normal polarity is now called the Matuyama Reversed Chron; and the transition between them is called the Brunhes–Matuyama or Matuyama-Brunhes reversal.
Source: “Motonori Matuyama”, English Wikipedia (CC BY-SA 4.0), excerpt