Character Analysis
Charles is the younger brother of Adam and the Cain to Adam's Abel (yes, everybody has a biblical double. Deal with it). Charles is the jealous type, the needy type, the violent type, the slovenly type, the dark and brooding type, and the stay-at-home type. But he's a whole lot smarter than Adam when it comes to recognizing the evil in people like Cathy.
Daddy Issues
Charles might be jealous for Cyrus's love and attention, but he really takes it out on his brother. It's weird, because you would think that Cyrus would love the son that is pretty much his clone:
His half-brother, Charles, only a little over a year younger, grew up with his father's assertiveness. Charles was a natural athlete, with instinctive timing and coordination and the competitor's will to win over others, which makes for success in the world. (3.2.4)
But no: try as he might, Charles is always Number #2 on his dad's favorites list. And with a competitive streak like that, it's no wonder that Charles flips out when Cyrus starts making it really obvious that Adam's the one he's going to groom in his image. Like, really flips out. Like almost-kills-his-brother flips out. That's some serious jealousy.
But Charles doesn't just have Adam to contend with. When he finds out that Cyrus died a suspiciously rich man, he also has to deal with the newly-discovered fact that the man he worshipped was probably a scumbag. Here's Charles's reaction:
Adam knew that his brother was no longer dangerous. There was no jealousy to drive him. The whole weight of his father was on him, but it was his father and no one could take his father away from him. (7.3.166)
See unlike Adam, who knows pretty much from the get-go that Cyrus is a lot of smoke and mirrors, Charles put Cyrus on a pedestal as a result of wanting his love so badly. Charles realizes that it's not really Adam he's mad at—as Adam says about the night Charles tried to murder him, "you were fighting for your love" (7.3.193). We didn't realize that you could fight for love with an axe, but there you have it.
C is for Cain
Alright, here is where things start to get weird. Aside from the blatant daddy issues, Steinbeck gives us a ton of signposts that scream Charles = Cain. Remember that weird moment where Charles seems fixated on the birthday presents that Charles and Adam got Cyrus? Charles got his dad a nice expensive knife, and it just sat in the drawer at home, while the mongrel pup that Adam picked up on the way home became Cyrus's boon companion for life. So why does this matter? Because in the biblical story of Cain and Abel, God rejects Cain's gift of a harvest but accepts Abel's gift of a lamb sacrifice.
In other words, it's hard for us to know why God likes lamb and not vegetables (how else are you supposed to get your fiber?), just like it's hard for Charles to know why Cyrus would like a dog but not a knife. It feels pretty arbitrary, doesn't it? And in a way, it is: Cyrus doesn't have a good answer for why he likes Adam more, and that makes it super frustrating for Charles.
But here's where things start to change from the biblical story: As we know, Charles doesn't kill Adam, but seems like he intends to when he beats him up and then comes back with an axe. Yikes. Instead, Charles senses some unfinished business, which he talks about in one of his letters to Adam:
Seems like to me there's something not finished. Seems like when you half finish a job and can't think what it was. Something didn't get done. (4.2.12)
And where does that unfinished business go? To the next generation of Trasks, Cal and Aron (whom, we find out, might be Charles's kids).
There are other ways in which Charles is Cain too: Like Cain, Charles is a farmer; and like Cain after God exiles him, Charles bears a mark that makes him self-conscious and shun other people. Allegories, people. Allegories.
Charles's Timeline