Julius Caesar 49 - 44 B.C.
Julius Caesar was the seminal figure responsible for the long line of emperors that would follow him. The complex events that led to his departure from the customary Republican ways of governing the country are beyond the scope of this short bio. Suffice it to say that a series of civil wars that shook Rome left the Senate weakened and actual power was wielded by only a handful of men. The traditional system of checks and balances that had up until then kept any one person from acquiring too much power was gone and, as is always the case, power hungry individuals moved in to fill the vacuum.
Caesar was one of those men who initially had carved up power with two other wealthy and influential men, Crassus and Pompey. Through a series of political maneuvers he eventually gained the upper hand and was able to edge out the other "Triumvirs" to become a de facto emperor. The key to his power lay in his systematic acquisition of titles that he wrested through one means or another from the Senate. Most important of these was the office of Dictator which until then was only sparingly given on terms that expired annually. The Dictator was given broad powers to rule during times of trouble and would be roughly equivalent to a military leader calling for a state of Martial Law. The scandal that precipitated his downfall was his brazen choice to name himself Dictator in perpetuity. In effect, this removed any possibility of others sharing in power while he remained alive and, to remedy the situation, a group of Senators led by his close friend Brutus stabbed him to death in the famous Ides of March plot (March 15th, 44 BC).
Caesar's assassination engendered a cascade of events immediately afterwards that, quite contrary to the hopes of his assassins, quickly evaporated the power of the Senate and its Republican ways for good. His life and death and the aftermath are memorialized in Shakespeare's Julius Caesar, one of literature's greatest plays.