Shmuel is Bruno's dream come true: He's a kid, a good listener, and he has the same exact birthday as our main man. But Shmuel is no ordinary boy—nope, he's a Jewish prisoner in Auschwitz. So even though he doesn't say so, we know he's seen horrific things. And because of this, while he and Bruno share a birthday, Shmuel is much more grown-up than Bruno is—Bruno may be pretty ignorant about the horrors unfolding next door, but Shmuel knows fear, starvation, and violence firsthand. In other words, as he's Bruno's friend and his foil.
If Bruno thinks his life blows, it's nothing compared to Shmuel's. While Bruno downgrades from a five-story house to a paltry three stories, prior to being held prisoner in a concentration camp, Shmuel explains:
"All I know is this […] before we came here I lived with my mother and father and my brother Josef in a small flat above the store where Papa makes his watches." (12.689)
In other words, even before life became truly terrible, Shmuel's life wasn't half as full of luxury as Bruno's. Importantly, this stems from their fathers' positions in society, positions which it seems fair to connect to their ethno-religious identities: Bruno's father is a German working for Hitler, while Shmuel's father is a Jewish man trying to hack it in an anti-Semitic world, even before the Holocaust begins.
Of course, once the Holocaust begins, trouble kicks into high gear for Shmuel and his family. By the time Bruno meets him, Shmuel's hardships have come to include:
If you're keeping score, by the time Shmuel and Bruno meet, the worst thing that we know has happened to Bruno is he's been forced to move away from his friends into a slightly smaller house. It's apples and oranges, really, which is kind of the point: Life is consistently easier for Bruno than his Jewish counterpart. If Bruno represents life in the bubble of childhood, Shmuel makes it clear that Jewish children all around him are being completely denied this experience. It's no wonder Shmuel always looks so sad.
Despite all the nasty stuff he's been through, Shmuel is the kind of guy you want on your side—he's sensitive, he's a good listener, and he's a loyal friend. And perhaps importantly for Bruno, Shmuel's not one to go on about the hardships he's experienced, thereby not shattering the bubble Bruno enjoys living in (more about this on Bruno's page elsewhere in this section).
While it may be tempting to look at Shmuel and marvel at his resilience in the face of forced adulthood, it's important to note that despite his pretty smooth veneer, he's still just a kid. The Holocaust may be able to force him to confront things far beyond his years, but it can't change the fundamental fact that Shmuel is still just a boy. This is perhaps never made clearer than in the moment when Kotler catches him eating some chicken that Bruno's just given him. When asked if he stole food from Bruno's kitchen, Shmuel responds by saying:
"No, sir. [Bruno] gave it to me […] He's my friend." (15.1029)
What Shmuel says is true—Bruno is his friend, and he has given him the chicken. But what's more interesting is that Shmuel fails to anticipate that Bruno won't back him in this moment. What this shows is that for all of his maturity, Shmuel is still a kid—he's not cynical or jaded or self-preserving, and while the Holocaust has consumed his family one member at a time, he still fundamentally trusts this little German boy who knows nothing about the camp experience. It is a childlike faith in friendship, demonstrating that in his heart, Shmuel is still just a boy.
And because we can see that Shmuel is just a boy, we're reminded of the ways in which he's similar to Bruno. For all that he knows that Bruno does not, he still yearns for company and readily aligns himself with his peers—just like kids do. In this, our attention is drawn to Shmuel's fundamental humanity. Yes, there are ways in which he operates as a symbolic counterpart to Bruno in this story, but underneath the trimmings and trappings of their respective experiences, a shared youthfulness—and in this, a common humanity—emerges.
In the end, then, when Shmuel stands in the gas chamber holding hands with Bruno, we don't find ourselves reading through the death of our main character and his symbolic opposite. We find ourselves watching two very young boys, from different walks of life and for different (though both totally absurd) reasons, preparing to die. Shmuel may pack a symbolic punch throughout the book, but when it comes to his death, the horror of the Holocaust is made all the clearer because he greets it as simply a boy with his friend.