The leading Korean car company's name rhymes with the first day of the week, as in "Hyundai, Bloody Hyundai." Which is pretty much what the company's competitors are saying to themselves these days about Hyundai's remarkable success over the past few years.

Last year Hyundai's global sales bucked the industry's decline and rose 5% to 4.2 million cars and trucks. Even in the U.S., the world's most competitive car market, Hyundai's sales rose 0.8% in the first eight months of this...