Gaius Julius Caesar was born most likely on July (originally Quinctilis, but renamed by Caesar in his own calendar reform) 13, 100 BC. Caesar was a member of the deeply patrician Julii family with roots dating to the foundation of the city itself. He later claimed to be a direct descendent of Aenaes, son of Venus, and therefore related to the gods themselves.
Still, at his start, the Caesar family was an impoverished line of the noble original clans. No Caesars in recent generations had held the seat of Consul but while still highly respected, they held little political clout. His father, Gaius Julius as well, had served in a respectable capacity within the Senate, but had little notoriety aside from his son's legacy. His mother, Aurelia, of the Aurelii Cotta line, seems to have been both a remarkable woman and a major impact on the life of her son.
Caesar was raised in the common quarters of Rome, or the Subura among the lower citizen classes. His home was what functioned as an apartment building in the modern world, or what was known as an insula. Even for a patrician family in poor financial straits, this was a definite handicap for future political ambition. However, the young Caesar certainly learned a great deal from his experiences as a child, as he early on realized the power in championing the common man. It wouldn't take a genius to understand that several politicians in this era made a name for themselves using this method, and Caesar certainly caught on to this easily. He had, though, the added advantage of his patrician heritage along with a sort of political genius that would push him to the very limit of Roman power.
Two major events impacted the life of the young Caesar. The later and seemingly less momentous event of the two was the death of his father at the age of 15 in 85 BC. So few of the details of Gaius Julius Caesar the elder's life are known, that it's difficult to determine the impact this may have had. While he certainly played a role in the life of his young son, he was often away on military and Senatorial obligations, as was often the case with Patrician families. His father had reached the office of Praetor prior to his death, the office just below Consul, and at least helped set the stage for the Caesar line to return to the highest order.
The more significant event in the life of Caesar was a marriage arrangement that would have enormous impact on Roman culture as a whole. The marriage of his aunt Julia to the novus homo (new man) Gaius Marius had repercussions that affected the entire ancient world. Through this marriage in 110 BC and 10 years prior to the birth of his famous nephew, Marius gained the political and familial connection necessary to advance his own career up the cursus honorum. While it may have been frowned upon by the elite of the day, first off in giving the uncouth Marius such assistance, it was a completely understandable move by the Caesars. Marius was certainly one of the richest men in Rome of the time and while he gained political clout, the Caesar family gained the wealth required to finance election campaigns for Caesar's father and uncles. As previously suggested his father attained the rank of Praetor and his uncle, Lucius Julius Caesar rose to a prominent Consulship during the Social War of 90 to 87 BC.
Marius' impact on the future dictator must have been immense. Their careers follow notable similarities that certainly show a profound influence by the uncle on the nephew. More importantly, however, Caesar had the great fortune of his patrician background which gave huge advantages over Marius. He also was able to play witness to both the successes and failures and adjust his own plans for the future accordingly. Marius was the pre-eminent Roman just prior to Caesar's birth, serving 6 Consulships, winning the war against Jugurtha, reforming the legions and the social order, and saving Rome from the Germanic Cimbri and Teutone threat. By the time Caesar was a young man, however, Marius had fallen deeply out of favor, though he was still a player of some note. As Caesar began his own career, he would be thrust into the coming conflicts between Marius and his rival Lucius Cornelius Sulla. The advancement of Caesar in light of the turmoil of the day is notable enough, the fact that he even survived may be even more remarkable.