Tyrants collect money and power, but they also amass bric-a-brac like the rest of us. What, if anything, do their material leanings signify?

Possible motives for collecting abound: compulsion, competition, exhibitionism, desire for immortality and the need for experts' approval. Peter York, a British journalist who studied dictators' decor for his book Dictator Style, recognizes all of the above in his subjects. It's basically a dictator's job, he says, to take everything over-the-top.

Stephen Anderson, professor of neurology at the University of Iowa, has come closest to finding a biological basis for the yen to collect. In 2004 he showed that damage to an area of the prefrontal cortex can lead to hoarding—the pathological cousin of collecting. Anderson doubts that's the case with the dictators. "Most people who have injuries to this part of the brain are not going to be successful," he says, "even in a bad-guy way." Still, he wouldn't be surprised if the bad guys' neural wiring were somehow amiss.

York has one more theory to add: the need for compensation. "Some of these people," he says, "were really very short."