I’m looking for a "Mrs. Watanabe."

Not just any Mrs. Watanabe — the Mrs. Watanabe, the archetypal financial journalist’s shorthand we’ve all used to discuss Japanese retail investors who dabble in forex trading. With the recent focus on the yen and a resurgence in interest in individual investing, the phrase — already one of the most common pieces of jargon in Japanese financial circles — has seen a resurgence.

That got me thinking: Where does the saying come from? Who coined it? Why is it Watanabe, and not a more common Japanese surname like Suzuki or Sato? And why is it Mrs. Watanabe, when data show that the majority of retail FX traders are men, as my colleague Shuli Ren has noted?