Ray Davis, Jr., left, and John Bahcall, right (circa 1966). Davis lead the effort to design and build the experiment which discovered the first solar neutrinos. Bahcall has spent much of his career building models of the Sun and computing how many neutrinos we should expect to see, which were consistently more than Davis' and others were actually detecting. The picture was taken in the Homestake mine, shortly before Davis' experiment began operating. The photographs are from Bahcall's extensive web site.
John Bahcall and Ray Davis at a meeting of the American Astronomical Society in Tucson, Arizona, January 1995. In spite of (or perhaps because of!) the disagreement with Davis' observations and Bahcall's predictions, the two have remained close friends and collaborators for over thirty years.