As much as I'm a fan of Caesar, I'd never call him a "good guy" because much of what he did would come across as completely self-serving and egotistical from our modern perspective. But his actions were in line with what other aristocratic Romans would do (or tried to do had they his power).

Just a few clarifications - the senate never appointed the first triumvirate, it was an unofficial grouping of Pompey, Caesar, and Crassus where they privately promised to look after each other's interest. The second triumvirate was an official entity (I believe sanctioned by the senate) with legal powers.

So to explain why Caesar did what he did, I need to explain Late Republican politics. Among the aristocracy, politics was a zero-sum blood sport. Your successes added to your family's prestige and built upon all of your ancestors offices and honours. Election to the office of the consulship was a physical manifestation of that prestige, demonstrating that you are the best among a very small field filled with fellow egomaniacs who all wanted to be the best. By the Late Republic this system, designed to work with a small city-state, was breaking down as it tried to run an empire. Aside from winning/losing prestige, men were lavishing extraordinary amounts of money to get elected and losing meant being millions in debt with no easy way to recover that money.

An earlier general/statesman, Sulla, had set the precedent that if the state (controlled or guided by your political enemies) did something you didn't like and you had an army that was more loyal to you than the Republic, you could march on Rome and push a reset button (and murder a few rivals) and set things the way you wanted. Sulla rewrote some laws to fit his view of the Republic and retired knowing he had demonstrated his authority over all.

The next three decades were filled with increasingly unstable politics: one attempted coup, political gang fights, widespread bribery, voter intimidation. It came to a head when a conservative faction wanted to limit the growing prestige of three particulars: Pompey, Crassus, and a relatively unaccomplished Casesar. Remember that this is a zero-sum game, offices and glory gained by Pompey would be denied others. So this broad faction began blocking anything these three men did - causing some loss of face.

To fight this and achieve their agenda, the three made the first triumvirate to get their goals made. But this was still within the framework of the Republic (they later would use illegal methods). So through various legal and some not-so-legal means they got what they wanted. One of these was Caesar got his appointment to be governor of northern Italy (Cisalpine Gaul). Caesar used some pretexts to involve himself in Gaul proper and, to make a long story short, conquered the living hell out of it.

As a result, he had a massive army that was very loyal to him, a massive amount of wealth, and enormous political clout. To the conservative faction he threatened to eclipse them all and dominate the political scene. By this time Crassus was dead and Pompey was aligning himself with the traditionalists but not completely hostile to Caesar. The civil war that followed was triggered by a seemingly unimportant administrative issue. Caesar had been given a set amount of time to govern Gaul at which point his power of command (his imperium) ended. He wanted to go from governor immediately to running for consul again - to cap off his illustrious career. Ostensibly another reason was to protect himself from prosecution by his political enemies for some of his actions in Gaul - you couldn't be brought before the court if you were a magistrate (e.g. consul or governor of Gaul). However I'm not sure this latter excuse holds water as he had such crazy levels of prestige and wealth, no jury could convict him. Regardless, settling affairs in Gaul was taking longer than he anticipated and Caesar got a special law passed that extended when he could be a candidate for consul.

The big question is did that extension have a specific date? Caesar said no, the conservative faction said yes. They demanded he give up his imperium and by extension his armies and return as a private citizen (without the immunity) and run for office. Caesar said no, the law issued by the people permits me to run in abstentia after the time the conservatives' deadline. I think many would agree that this war came about over Caesar's refusal to suffer a loss of face. Note that if not Caesar, probably another general would have taken the steps to trigger a civil war - the Republic was pretty much imploding at the time.

So civil war comes and Caesar beats Pompey and the Republicans. He returns to Rome and is appointed dictator by the senate - a position with along history. This was a special office for emergencies or to hold special elections (e.g. both consuls had died in war and they needed a senior magistrate to preside over the elections) and after fixing some stuff he laid down the office. He was then elected dictator again but this time for life. Now, how willingly was this done by the senate? They'd just been through decades of civil unrest followed by an actual civil war and Caesar seemed to bring peace and stability. But at the same time he still had a massive army that was still completely loyal to him and had trounced the Republican opposition on the battlefield. Many senators had fought on the Republican side and had been forgiven by Caesar (contrasted with Sulla's murder of his political enemies) - so many undoubtedly had a sense of obligation to the great man. Was this a rubber stamped PR exercise or did they legitimately vote it for him? Maybe both? Who knows?

I'm hoping one of the experts comes by and critiques this, I'm sure I'm missing some nuances or abbreviating things a bit too much.

Well, if you're apologizing for that paragraph, I guess I'll apologize in advance for my writeup! Buckle up, 'cause we're gonna go for a bit of a ride through Rome in the 1st century BCE. Note - by Julius Caesar's time, Rome was basically on the cooling off period from the previous bunches of civil wars. The big issue with those civil wars is that they...well....didn't really fix anything. In the first post, as per usual, I give background to Caesar and the environment in which he lived :) If you'd like to get straight to the meat of your question, head down to the next post!

The first of those wars was the Social War. Rome, after the Third Punic War had finished, had a huge amount of territory under her control. The city controlled the Mediterranean, and while that control would be expanded under Pompey, the city controlled territory from Spain to North Africa to the Italian Peninsula to Greece and even Pontus in the far East. Their greatest allies through that tumultuous century of war had been the Italians, who had also borne the brunt of Hannibal's invasion and who had provided a constant stream of men for the Roman military. Despite all of that, they basically were seen as "second-class citizens" of a sort, without any of the rights allotted to the citizenry of Rome. Their aristocracies were mostly Roman due to intermarriages, but the people themselves wanted to be seen as Romans. Rome refused to give them those rights, and so the people revolted. Despite only lasting a couple of years, that war was extraordinarily bloody and consisted of Roman armies fighting Roman armies for the first time. Rome quickly established peace by enfranchising the Italians (except for the Cisalpine Gauls) with citizenship. Most people, as you can imagine, saw the war and waste of lives as a pointless endeavour. But hey, what can you do, right?

And then came the politics. First century politics are basically a mess where people made things up as they went, while still trying to stick those onto old traditions, so if you get confused here, please feel free to ask questions :) The time period is 88 BCE, and the social war has just ended. The two pre-eminent generals in that war weren't too fond of each other, despite having worked together on other occasions. Caius Marius was the older of the two, and perhaps one of the most distinguished men of the period at that point. He had served an unprecedented 6 straight consulships (you were supposed to wait 10 years between each one, but he was elected 6 times in a row), and, as a result, he commanded an immense amount of respect. Yes, this might seem like a tangent. The Roman concepts of auctoritas and dignitas, however, cannot be understated in its importance, and it directly links to what you're asking. I'll discuss dignitas in just a little bit - I can't find which of my posts talked about it, so I'll write something up below.

So the thing about auctoritas and dignitas was that they were passed down through family lines - the more distinguished your ancestors were, the more people would listen to you. Roman politicians always wanted more. They wanted more recognition, more power, and more awards; they didn't want them purely for the power (though that was surely a factor), either. Instead, they wanted the glory. The glory those honours would bring to their family was incredible. Marius himself was a new man - he had no distinguished ancestry, and he was brought up in a poor(er) household. His being elected consul once was an incredible feat, and he was elected for an unprecedented 6 times in a row. As previously noted, though, Roman politicians always wanted more. According to popular legend surrounding him...

When, that is, he was quite young and living in the country, he had caught in his cloak a falling eagle's nest, which had seven young ones in it; at sight of this, his parents were amazed, and made enquiries of the seers, who told them that their son would be most illustrious of men, and was destined to receive the highest command and power seven times.^1

He wanted that seventh consulship. Unfortunately for him, one of his political allies decided to start up a rebellion of his own during Marius' 6th consulship. Marius quickly put it down, but that kind of a smudge on his reputation was a political anchor, and he wasn't able to secure another election. He lost, but still had enough political clout to get things that he wanted. And oh, did he ever desire more glory. Mithridates of Pontus had just rebelled, and Pontus was an extremely rich state. As a result, everyone wanted to command Rome's war there - victory was never in doubt. The Senate, which was the body responsible for assigning provinces to the consuls depending on Rome's need, assigned the Eastern Provinces (Greece/Pontus) to Marius' rival: Lucius Cornelius Sulla. Marius basically threw a tantrum, inducing one of his allies among the tribunes to hold a popular vote, rather than to have the matter settled in the Senate. The people, who were always fond of Marius, voted to give him the command, rather than Sulla. And Sulla had just recruited 6 legions with the promise that those legions were headed to war in the east, those legions were going to get rich, those legions would be awarded land at the end of their tenure, and...most importantly...Sulla would be the one who would get all of the credit and glory from Rome's victory over there.

Yeah, let's just say that Sulla was rather pissed at this. Not only had Marius usurped his command, which he'd already spent a considerable amount of money on, but that meant his troops were basically going to get nothing and go nowhere. Sulla himself was going to have to do nothing at all, while Marius just reaped more glory for himself. Needless to say, Sulla wasn't going to stand for this at all, and he, apparently, told his legions what was up and they "convinced" him to march on Rome and "correct the Marian takeover."

And so, for the first time in Roman history, a Roman army marched into Rome. Marius and his supporters fled the city into exile (in North Africa), and Sulla was granted the command in the East (again). Not too bad, right? Right?

Well, Marius still really wanted that glory and that seventh consulship. And it just so happened that all of Marius' old veterans had been settled in North Africa (which was extremely fertile, good, very expansive land). And hey, they would follow their old general to the gates of Hell if he asked. Marius mustered up an army of his own and marched on Rome. Sulla, in the East, was busy fighting a war and was unable to come to Rome's aid, and Marius took over Rome. He started a brutal culling of all of those who supported Sulla, displaying their heads in the Forum, and, according to our sources, while he was only alive for a short period of time after taking the city, the city became a hive of rampant murder.

Sulla heard about all this and headed back to Rome with his army (which had just finished beating the crap out of Mithridates). While he was on his way, Marius died in the midst of hallucinations and delusions - possibly a panic attack caused by these.

When Sulla got to Italy, another major civil war ensued, with the Marians getting kicked around the Italian peninsula and eventually retreating to Spain, where Sertorius held out for some time. But when Sulla got to Rome, he was no more gentle than Marius had been - he proscribed (put bounties on) thousands of people, had himself "elected" as dictator, and set about trying to fix the problems that had led Rome into a decade of civil conflict. While the dictator was only supposed to stay in office for 6 months, Sulla had no time limit imposed on his own dictatorship. He resigned after about a year, thinking that everything was put in its place, and died shortly after from natural causes (you really don't want to know, it's a rather nasty disease).

1. Plutarch, Life of Marius (36.5)

I think you're a little confused. First, Caesar didn't appoint himself dictator - only the Senate could declare a dictator. Now, it may be Caesar managed to pack the Senate with his partisans or intimidated them with his army, but the procedure was constitutional by Roman standards. Second, the Triumvirate of Pompey, Crassus, and Caesar was never formal. It was a gentlemen's agreement. The confusion arises because the Triumvirate of Octavian, Antony, and Lepidus WAS a formal appointment. Historians project the name of the formal appointment onto the earlier, informal relationship.

As to why Caesar wanted to be dictator, well when he arrived in Rome in 49 BCE both consuls had fled to Greece. There was no one to administer elections. Caesar held the dictatorship for holding elections and appointing governors etc. He resigned that after 11 days. Why he accepted the position for ten years and then perpetuo I don't know. About being a "good guy," a) Caesar is such a fascinating character because 2000 years later it's impossible not to have an opinion about the guy, and b) I don't think many historians go in for that kind of judgment anymore.

Thanks to everyone who answered! This really helps, my book didn't mention the Triumvirate being informal or the fact that the Senate appointed him, it just said that Caesar made himself dictator and that kind of confused me. I guess there only so much they want us to learn...

Again, thanks, this subreddit is amazing!