Berthold Schweizer was born in Germany to a Jewish family that emigrated to the USA in 1937. He became interested in mathematics as a child, and studied in the Massachusetts Institute of Technology (BSc 1951) and at the Illinois Institute of Technology in Chicago (MSc 1954). At this institution, he earned his PhD in 1956 under Karl Menger. Berthold Schweizer had a long and successful academic career. He taught at the Naval Ordnance laboratory (1951), IIT (1956–1957), San Diego State College (1957–1958), UCLA (1958–1960), the University of Arizona (1960–1965 and 1968–1970), and the University of Massachusetts at Amherst (1965–1968 and from 1970 until his retirement in 1996). He had several visiting appointments in Vienna, Perugia, Barcelona, Lecce, Bern and Beijing. He was a superb expositor and a motivating teacher.
He was the adviser of 12 PhD students and also mentored many post-doctoral students and visitors from the USA and various other countries.
Berthold Schweizer and Abe Sklar were the founders of the theory of probabilistic metric spaces, a concept introduced by Karl Menger in 1942 that Schweizer, Sklar and their students developed. It was in this mathematical elaboration of the theory of probabilistic metric spaces that Schweizer and Sklar developed a remarkable body of new mathematical machinery, using techniques from the theory of functional equations and inequalities, and making important contributions to the study of the associative functions in real intervals (t-norms, t-conorms) and the theory of copulas (created by Abe Sklar).
Berthold Schweizer wrote many papers and some fundamental books, working always with Abe Sklar or his students. In his last years, he was working with Abe Sklar on Menger's legacy and a new project concerning what they called the grammar of functions.
It is interesting to note that, beyond the interest in probabilistic metric spaces, Schweizer's work had a profound impact in other fields: functional equations; inequalities; fuzzy sets theory; mathematical models in economics; etc.
Berthold Schweizer was a great mathematician, a loving husband, father and grandfather, and a very warm, open, and generous man. I had the opportunity to work with him in 1976–1977 and since then have had the pleasure of undertaking scientific work with him for more than 32 years and developing a close personal relationship. He was an inspiring adviser and a wonderful person. We will miss him very much, but our good memories and his mathematical creativity will remain with us for years to come.