I'll give you a brief answer on at least the origins of the term.

The first dictators were from ancient Rome. It was a position that went with the standard consuls, quaestors, praetors, etc. However, the dictator was apart from those positions. Dictators were a special position only put into power during times of great stress on the Republic. They were given practically full control over the Republic for a brief time (I believe usually terms of around 6 months) in order to guide Rome through hard times. Upon succeeding, they were expected to step down and relinquish power back to the Republic. This actually worked fairly okay, up until some guy by the name of Julius Caesar modified the role to establish himself as a lifelong dictator.

I won't give a slew of examples of the change in dictator over time, but you can see that even the inventors of the term changed it into pretty much what it is today, a lifelong position of autocratic power.

Lucius Quinctius Cincinnatus is possibly one of the best examples of the ideal Roman dictator. The story goes that he was an old man at the time working on his small farm. After an invasion, Rome scrambled for somebody to handle the problem. They approached Cincinnatus with the offer of being dictator to guide Rome through its troubles. According to the legend, he dropped his plough in the field and went at once to attend to the needs of Rome. After successfully guiding Rome out of the trouble, Cincinnatus gave up his near autocratic power immediately and returned to his farm and plough. Originally, dictators were supposed to work for the good of the Republic not for selfish means. Understanding how human nature works, it isn't suprising that this ideal didn't last long.