The Mystery Man

This mystery man appears in both Flight 714 in a phone conversation with Spalding (pages 6 and 8) and in The Red Sea Sharks (pages 15 and 16 ).

Or so we suppose from the color of his hair, his general size and shape, the hat style, glasses and cigar. His name appears to be Walter, if Spalding is talking to him, as we assume.

Who is this Walter? Does he appear in any other books?