It seems that almost every where that physics is taught, in particular teaching relativity or quantum phenomena, that examples or demonstrations using persons Bob and Alice is a common tradition. Professor Susskind uses Bob and Alice quite a bit in his ER=EPR lectures. Several text books I have on relativity, both special and general, use Bob and Alice in various diagrams usually highlighting their respective world lines.
I am curious. Who started this, is there a first example using Bob and Alice?