what the (blue) blazes

An exclamation used to emphasize surprise, shock, anger, disgust, etc. In this phrase, "the blazes" is used as an intensifier. The phrase can also be used with other question words (e.g. "who," "why," "how," etc.). What the blazes are you doing? You can't come in here! What the blue blazes? I just had this fixed, and now there's a dent in it! Just what the blazes is going on here?