ABSTRACT
Before I met Yakov Zeldovich for the first time in June 1980 on the occasion of the COSPAR meeting in Budapest, I had hardly paid attention to his name, which I first read on the cover of the famous Relativistic Astrophysics, whose formulae at first sight rebuffed me until I found them and the text around them to be astonishingly clear. I also knew of him because of his association
with my great friend Sunyaev, through the famous effect which carries both their names, and which allows in principle to determine the distance to clusters of galaxies through a
combination of X-ray and submillimetric observations, thereby allowing an unbiased determination of Hubble’s constant.
