Robert T. Beyer was a major contributor to our understanding of ultrasonic relaxation processes in liquids and solids during the heyday of that field. One could argue that this period ran roughly from the time of his major review article in 1951 [J. J. Markham, R. T. Beyer, and R. B. Lindsay, Rev. Mod. Phys. 23, 353--411 (1951)] until his monograph in 1969 [R. T. Beyer and S. V. Letcher, Physical Ultrasonics (Academic, New York, 1969)]. He adopted and extended new measurement techniques of ultrasonic attenuation and used them to advance our understanding of relaxation processes in liquified gases, in water and aqueous solutions, in organic liquids and organic single crystals, and in liquid metals.