Fiyero is only featured heavily in Volume 3, but his presence dominates the entire latter half of the book. He plays the all-important role of love interest to the lead character, but he's doing more than just being "the boyfriend" here. Fiyero gives us insight into Elphaba's character and the political nature of Oz. Plus, it's through Fiyero that we meet a number of the book's significant characters (namely Sarima and her family in Kiamo Ko).
Fiyero's status as a Vinkus Prince is hugely important in this book. His foreignness is actually the first thing that's emphasized about him:
And so it seemed, a student from the Vinkus, in strange ceremonial garb, coming late for class, opening the wrong door, confused and apologetic. (188.8.131.52)
After his initial introduction, we learn almost nothing of Fiyero outside of his foreign status. He's the classic foreign exchange student, around to explain things about his culture and to provide us with scenes of mild culture shock.
It's not until Volume 3 that Fiyero is fleshed out as a character, and much of that characterization is in relation to Elphaba. So is Fiyero a significant character in his own right? Read on…
The third volume is told exclusively from Fiyero's point of view, even though the events of this volume play a huge role in shaping Elphaba's character. We actually never hear Elphaba's take on her affair with Fiyero. But we do see the effects of his loss on her character in the latter volumes of the book.
Elphaba is shaped by many longings in her life: for Frex's attention, for Nessa's shoes, for meaning. Actually, all of those things can be lumped together under Elphaba's desire to matter. The other major thing that shapes her adult life is her guilt and her desire for forgiveness. It seems that Elphaba wants to mean more than her guilt, more than the disastrous end of her relationship with Fiyero. She never wants to mean more than being with Fiyero, however.
Elphaba and Fiyero are greatly defined by their relationship with one another. It's not until Fiyero embarks on a relationship with Elphaba that we actually get to know him. The two really are perfect for each other – they challenge one another, can handle each other's flaws, and love each other.
But Fiyero is more than just the co-star of a tragic love story. He's an interesting individual who's going through a lot of changes, which are represented by his relationship with Elphaba. Fiyero acts like a window for readers; it's through him that we experience a gradual awakening: to love, to politics, to adulthood. Fiyero learns about the world around him when he's with Elphaba:
He wanted to tell Elphie what he had seen, but he held back for reasons he couldn't name. In some way, in the balance of their affections, he sensed she needed an identity separate from his. Were he to become a convert to her cause, she might drift away. He did not dare risk it. But the vision of the battered Bear cub haunted him. (3.12.1)
This scene is really fascinating. We never see Elphaba's political awakening or have access to her internal thoughts during her transformation into a rebel. For Fiyero, though, we hear his inner thoughts upon witnessing an injustice, and in the aftermath of this injustice. Unfortunately, the ultimate injustice of Fiyero's life is his tragic death.
In a way, it's Fiyero, and his death, that guides Elphaba towards becoming the Wicked Witch of the West. Fiyero is a powerful presence after his death, perhaps more powerful than any absent but still alive character. Part of his presence might stem from the fact that his death is so ambiguous. We never actually see Fiyero die, and even Elphaba is convinced at one point that he might still be miraculously alive. (He isn't.)
Fiyero is in some ways overshadowed as a character by his own death and by his impact on Elphaba's life. But he's definitely an individual in his own right; he's more than just the tragic Mr. Elphaba, and his role in the book is a significant one.