Frederick II "the Great" of Prussia is often portrayed as a devoted patron of the arts. A polyglot and an accomplished musician, he corresponded with many of the important philosophers and intellectuals of his day. However, his views on mathematics show a completely different side of his character. Shortly after his accession to the throne in 1740, as part of his restructuring of the Berlin Academy of Sciences he employed the eminent mathematician Leonhard Euler to lead its Mathematical Class. But, though he clearly recognised the need for mathematics, Frederick's derision towards the subject did not make for a happy working relationship between Euler and his patron. Matters were not helped by incidents such as the oft-cited failure of Euler's designs for fountains at the royal palace of Sanssouci. Letters from Frederick to Euler and others reveal not only an intense dislike of Euler on a personal level, but also a petulant contempt for mathematics and mathematicians. Having such a difficult patron undoubtedly made life difficult for Euler. In this talk, I will explore some aspects of the relationship between Euler and Frederick, and investigate Frederick's role as a less than enthusiastic patron of mathematics.