With what started as a republic, the empire soon grew into the ruling force throughout all of Rome. The imperial chain of command began with the Emperor, often a figure that was considered a god, either by force or will. This leader was guarded by a special military division called the Praetorian guards who are somewhat like today's secret service of the USA. Along side the Emperor was the Senate, comprised of about 100 noble men, which voted for or against certain "bills" that were brought before them. They had some say although really held no powers as the Emperor could always overthrow them at his own will.
As said above, the emperor was the most important figure in the imperial chain of powers. Some claimed to be descendants of gods, some were pyromaniacs, and others were lame and had a stutter. Lucky for most of them they weren't voted in like a republic but title was passed by liniage through blood, and in some cases, adoption.
To see a list of emperors and get more information for them please click here --> A list of emperors