Oliver de Boys is the oldest son of Sir Rowland de Boys, which makes him the older brother of Orlando and Jaques de Boys (not to be confused with Jaques the melancholy clown). Because he's the oldest, Oliver has inherited just about all of his dead father's fortune and he's also been put in charge of looking after his little brothers.
You probably noticed that Oliver isn't exactly the nurturing type. In fact, he's kind of a jerk. He treats his little brother Orlando like he treats his servants, refuses to pay for Orlando's schooling, and never gives the kid any walking around money.
Oliver's bad behavior toward his brother hints at larger social issue – primogeniture, or the system in which all of a father's wealth, land, and titles are passed down to his eldest son. (Yep, that means that any sisters or younger brothers totally get the shaft.) Shakespeare is really interested in the kinds of problems primogeniture can create. It comes into play in King Lear (where Edmund is so bitter that he tries to destroy his older half-brother) and also in Henry IV Part 1 (where King Henry worries that his son, Prince Hal, is waiting for his him to hurry up and die so he can inherit the crown).
Still, Oliver's not just a tightwad – he's also a would-be murderer because he tries to have Orlando killed by the court wrestler, saying he'd just as soon have Charles "break [Orlando's] neck as his finger" (1.1.18). Yikes!
So, what, if anything, motivates this character? For the answer, let's turn to Oliver:
[...] I hope I shall see
an end of him; for my soul, yet I know not why,
hates nothing more than he. Yet he's gentle, never
schooled and yet learned, full of noble device, of
all sorts enchantingly beloved, and indeed so much
in the heart of the world, and especially of my own
people, who best know him, that I am altogether
It's pretty obvious he hates his little brother because Orlando is inherently good and people like him more than they like Oliver. So, Oliver is petty and jealous, at best, which makes him a classic example of the "bad brother."
Literary critic Anne Barton says Oliver's petty jealousy also makes him a lot like the "bad witch" figure in fairy tales. We have to agree. When you think about it, there's not much difference between Oliver and, say, the evil queen who wants her pretty step-daughter dead because a magic mirror says "Snow White is fairest of them all." (The same can be said of Duke Frederick, who kicks Rosalind out of court because she's more popular than his daughter.)
In other words, Oliver is mean-spirited and hateful for no good reason, which means his character doesn't have much depth. This becomes even more clear when Oliver undergoes a sudden "conversion" in the Forest of Arden after his little brother saves him from a "green and gilded snake" and then a "hungry lioness" (4.3.5-9). What? You want to know more about this snake and lion business? Fine, go to "Symbolism" and check it out.