Because Nostromo is the title character, you'd kind of expect him to be the main focus of the book from the very beginning. However, that's not exactly the case. When the book opens, we lot of details about the setting and political and economic interests at work in the fictional country of Costaguana. In fact, we learn a heck of a lot more about the silver titan Charles Gould within the first few chapters than we do about Nostromo—weird, right?
Also, the first information we do get about our "hero" comes to us second-hand and kind of in passing, offered as secondary details in a larger story about Costaguana political brouhahas. Captain Mitchell, the head of the Oceanic Steam Navigation (O.S.N.) company, mentions that Nostromo played a key role in helping President-Dictator Vincente Ribiera get out of town quickly when he was fleeing a revolutionary mob, but that story quickly shifts focus back to Mitchell's own role in the crazy caper:
"Providentially, Nostromo—invaluable fellow—with some Italian workmen, imported to work upon the National Central Railway, was at hand, and managed to snatch him away—for the time at least. Ultimately, Captain Mitchell succeeded in taking everybody off in his own gig to one of the Company's steamers—it was the Minerva—just then, as luck would have it, entering the harbour." (I.2.10)
Wow. Even when Mitchell is waxing poetic about Nostromo's awesomeness and "invaluableness", the underlying message is really about how awesome Mitchell is for having found and hired Nostromo.
Just check out Mitchell's description of Nostromo's efforts to defend President Ribiera and local businessmen and administrators (including himself) from violence during those political upheavals:
"Under providence we owed our preservation to my Capataz de Cargadores, as they called him in the town, a man who, when I discovered his value, sir, was just the bos'n of an Italian ship, a big Genoese ship, one of the few European ships that ever came to Sulaco with a general cargo before the building of the National Central. He left her on account of some very respectable friends he made here, his own countrymen, but also, I suppose, to better himself. Sir, I am a pretty good judge of character. I engaged him to be the foreman of our lightermen, and caretaker of our jetty. That's all that he was. But without him Señor Ribiera would have been a dead man." (I.2.13)
"That's all he was"? In the words of Cher from Clueless, "That was way harsh."
So, yeah, lots of compliments and details about Nostromo here, but do you notice how Mitchell refers to the sailor as his Capataz, someone he "discovered"? This early moment sets us up to see Nostromo as a supporting player in other people's stories. Which is really weird, since the book is named after him.
Despite the fact that the narrative shoves him aside early in the novel, Nostromo is no joke. Everyone seems to agree that you don't want to cross him; he is known around town for being quite the tough guy.
Again, we have to go to Mitchell for some details about Nostromo's reputation, which helps keep people around Sulaco in line:
"This Nostromo, sir, a man absolutely above reproach, became the terror of all the thieves in the town. We were infested, infested, overrun, sir, here at that time by ladrones and matreros, thieves and murderers from the whole province. On this occasion they had been flocking into Sulaco for a week past. They had scented the end, sir. Fifty per cent. of that murdering mob were professional bandits from the Campo, sir, but there wasn't one that hadn't heard of Nostromo. As to the town léperos, sir, the sight of his black whiskers and white teeth was enough for them. They quailed before him, sir. That's what the force of character will do for you." (I.2.13)
Do not cross Nostromo. He's a terror with a force of character (a force of terraracter? No?) and has scary black whiskers and white teeth. He's basically a werewolf.
As the novel progresses, Nostromo becomes more and more central to the action. He really takes center stage when he is asked to help Martin Decoud get a hefty shipment of Charles Gould's silver out of town prior to the arrival of revolutionary forces in Sulaco.
At this point, though, Nostromo has grown pretty tired of being treated as a simple tool or errand boy for the local European population, and he really resents that he's been given a mission with such a low probability of success. He says as much to Martin:
The Capataz, indifferent to those dangers that seemed obvious to his companion, allowed himself to become scornfully exasperated by the deadly nature of the trust put, as a matter of course, into his hands. [. . . ] "Señor," he said, "we must catch the steamer at sea. We must keep out in the open looking for her till we have eaten and drunk all that has been put on board here. And if we miss her by some mischance, we must keep away from the land till we grow weak, and perhaps mad, and die, and drift dead, until one or another of the steamers of the Compania comes upon the boat with the two dead men who have saved the treasure. That, señor, is the only way to save it; for, don't you see? [. . .] This thing has been given to me like a deadly disease." (II.7.161)
As Nostromo goes on to say, they're asking him to take this huge risk for a supply of silver whose loss, at the end of the day, would not "have impoverished Don Carlos Gould very much" (II.7.163).
So, even he becomes more of a central focus for the narrative, Nostromo is still being treated as disposable in this larger tale of political maneuvering, and it's starting to get on his nerves. Of course, as Martin becomes aware, Nostromo is less upset about the prospect of dying and more ticked off that failure to rescue the silver would damage his legacy/reputation—he's very vain about his reputation.
Despite the odds, Nostromo manages to escape death and rescue the silver, burying it on the Great Isabel (an island off the coast of Sulaco). No one else knows that Nostromo has it; someone else mistakenly reported that it was lost for good, and Nostromo doesn't correct that impression when he gets the chance. He just kind of stays quiet and twiddles his thumbs.
After some additional hijinks and one more dangerous mission (one that is key to defeating anti-revolutionary forces and achieving the secession of the independent Occidental State), it begins to look like Nostromo might get everything he wants: status, money, and respect. He might, to paraphrase David Copperfield, actually get to be the hero of his own story for once.
Unfortunately, Nostromo's early comparison of the silver as a disease turns out to be pretty apt, and his obsession with it soon takes over like a nasty rash. He basically becomes just as nutty about the silver as Charles Gould was when he sent Nostromo off on that mission he resented so much. Ah, irony…
Like Charles Gould, Nostromo starts treating the silver like a secret girlfriend. To help ensure that its existence remains a secret, he sets up the woman who is supposed to be his real girlfriend and her family as caretakers of the lighthouse on the Great Isabel—since he could damage control the situation pretty quickly if they, say, happened across the silver.
You'd think that, with a flesh-and-blood girlfriend and a secret stash of silver, Nostromo would have his hands full. Nope. Partly out of lust and partly because he feels he can trust her with his secrets, he strikes up a romance with Giselle, the (ouch) younger sister of his fiancée, Linda.
This sets off a chain of events that ends with Nostromo getting shot when Giselle's father, Giorgio, mistakes him for one of Giselle's other suitors, who was thought to be prowling around without permission. Naturally, Nostromo had actually been prowling around to visit the silver on this particular occasion. This is all especially sad because Giorgio and his late wife had always thought of Nostromo as their son.
After being shot, Nostromo summons Mrs. Gould to his bed and offers to tell her where the silver is. Since she found its existence as much of a drag as Nostromo did, she says she doesn't care about the silver. So, the secret dies with Nostromo…
Oh, and by the way, Nostromo's real name is Giovanni Battista Fidanza. Nostromo is an Italian word for boatswain—but also, more importantly, it's a bastardization/mispronunciation of the Italian phrase "nostro uomo," which means "our man." So, like Mitchell with his "my Capataz de Cargadores," this nickname once again makes Nostromo a possession.