Someone calling himself The Calendar Man challenges Batman in the newspaper: he will commit one crime a day, for five days, each based on a season, unless Batman can stop him. Five seasons? For each crime, the Calendar Man is wearing a different costume, but Batman can stop only some of the crimes. On the fourth day, Batman realizes the fifth season is the Indian Monsoon season, and a magician called Maharaja is revealed as the Calendar Man.
Since he's come back a few times since, it seems many people like the Calendar Man, especially the gimmick of wearing a different costume for each crime he commits, but no one can figure out how to make him into a more prominent Bat-villain.