Harry Barkus Gray (born November 14, 1935) is the Arnold O. Beckman Professor of Chemistry at California Institute of Technology.

[3] After that, he spent a year (1960–61) as an NSF Postdoctoral Fellow at the University of Copenhagen,[4] where, along with Walter A. Manch, he collaborated with Carl J. Ballhausen on studies of the electronic structures of metal complexes.

[8] Gray's interdisciplinary research program addresses a wide range of fundamental problems in inorganic chemistry, biochemistry, and biophysics.

[9] Over the past twenty-five years the Gray group has been measuring the kinetics of long-range ET reactions in metalloproteins labeled with inorganic redox reagents.

Early research by his lab members showed that details of the internal structures of the proteins dominate the ET rates.