The fall of the Roman Republic was more than one man or one event.  Massive and rapid expansion until the mid 1st century BC revealed severe flaws and disagreements in the political philosophies as well as serious governing, and administrative inadequacies within the Roman Senate.  Periods of stability were mixed with those of near collapse while powerful Generals, co-conspirators and  inciters were constantly maneuvering for political power and position.

The social inequities and corruption that resulted from a fragile class system gave rise to demagogues such as the Gracchi brothers that used citizen assemblies to disable the legitimate power of the Senate.  The Roman Senate with the its patricians (inflexible and the ruling power) stubbornly retaining  power and the plebeians looking for a greater share of governance was steadily stumbling toward a momentous clash between factions.

In the mid 1st century BC, 3 men, Julius Caesar, Pompey and Crassas formed a secret pact – the 1st Triumvirate to control the Republic.  After Caesar’s conquest of Gaul, a standoff between Caesar and the Senate led to civil war with Pompey leading the Senate’s rebellious forces.  Caesar defeated Pompey and was made Dictator for life.  The dissenting Senators assassinated Caesar because of his absolute power and they violently opposed a return to a Monarchy. The Senate continued its demand for a constitutional government.  A 2nd Triumvirate agreement consisting of Caesar’s heir, Octavian, Mark Anthony and Lepidus was a secret attempt to avoid all-out civil war. 

Caesar was not the only man causing the fall, but certainly had a part in the demise. His assassination and the continuing civil wars that resulted would now require a similar leader who could again motivate the Empire and possess the command to create the necessary organization and control to save the greatest empire in the world from committing its own demise.  The assassination of Julius Caesar had clearly demonstrated how intractable conditions in the Empire had become.   
The Roman Empire Rome was in need of a single leader to assume dictatorial authority and stabilize the Empire.  .

In the ensuing struggle for power, Octavian defeated Anthony and Cleopatra at Actium in Egypt, Lepidus was exiled and Octavian became the undisputed ruler of Rome.

The eventual rise and confirmation of Caesar’s heir Octavian to the exalted post of Augustus Caesar spelled the End of the Roman Republic.  It was Augustus who proved to be the man powerful enough to control the Senate, the Roman Legions and the mob.  Gaius Caesar Octavian’s Augustus rose above all the great Roman Emperors before him to outlast his opponents, reform a corrupt government and stabilize a system that was in chaos.

The fall of the Republic was inevitable, but fortunately for Rome and the Romans, the right man at the right time was there to become the First Roman Emperor.