Who proved Haag's theorem?

In physics literature, there are several different characterizations of Haag's theorem and its consequences for quantum field theory. These different versions of Haag's theorem are due in part to various generalizations and more "rigorous" proofs of Haag's theorem as well as to the fact that many of these proofs were done using different formulations of quantum field theory. As a result, there is confusion about what Haag's theorem is and when it was proved. This paper clears up some of these confusions by examining the history and development of Haag's theorem up to 1959. It is argued that the question of who proved Haag's theorem is tied up with what the theorem is taken to show.