The Double Spy by Dan T. Moore
"Meet the man with no name. Nothing cool about this cat. He was built along the lines of a necktie rack, weighed slightly more than a used napkin, and was as shy as the ante in a crooked poker game.
No sex appeal there, you'd say. Yet within the space of a few days every woman in the country melted into quivering protoplasm at the very thought of this mystery man!"