Born in Berlin in 1926, Rotar drove a tank during the Second World War. After the war he trained as a cabinetmaker, then went on to study painting as well as furniture and interior design in Cologne and Bremen.

In 1947/48 he first began to deal with the spiral in his artistic works. His work as interior designer and manager at the newly established furniture design firm Knoll in Stuttgart, and from 1957 in Düsseldorf, brought him into frequent contact with contemporary artists such as Joseph Beuys and James Lee Byars, with architects like Mies van der Rohe, as well as with the leading gallery owners and art dealers of the 1960s. Rotar was by all accounts an introvert, but maintained long relationships with certain of his acquaintances, especially Beuys and Byars. From 1973 on, Rotar decided to devote himself exclusively to his painting and photography.

Over the years he distanced himself more and more from the art market, and died unexpectedly in August 1999.