Rudolf Peierls was a key member of the Tube Alloys, Britain's nuclear development program, and later of the Manhattan Project. Together with Otto Frisch, he was the first to propose that by using an isotope of uranium, the atomic bomb can weigh pounds, not tons. That proved to be quite useful...

Was Peierls a Jew?

He had a Jewish father, a Catholic mother, was baptized Protestant, and had to leave Germany because of that whole Jewish thing. As an adult, he ditched religion. So let's say "Borderline Jew".

Was Peierls a spy?

This one is harder to answer. The big blotch on Peierls' resume was his recruitment of fellow German Klaus Fuchs for the Tube Alloys. Fuchs turned out to be a major Soviet spy. There is also a bunch of supposed evidence to accuse Peierls, so much so that he lived under suspicion for the rest of his life after Fuchs was exposed.

However, most of that evidence is very circumstantial, so let's say... "Barely a Spy"?