Buttercup's motivation before she falls in love with Westley and then after she believes Westley dead, is virtually nil. She moves complacently through her days, certain that she will never feel passion for anything or anyone again, but willing to go through the routines and rituals involved in becoming queen. The greatest factor in her decisions is a simple preference of life over death—she marries Humperdinck instead of opting for death, and she jumps into the shark-infested water rather than have her throat slit by Vizzini. Once she loses Westley after the Fire Swamp, she spends the rest of the story desperately trying to bring him back. In her essence, Buttercup is a common girl who also happens to be bold, passionate, and uncommonly beautiful, and in the end it is her beauty that moves the men who move the plot, not her wits or courage. The Buttercup in the book is less guarded, less rational, and more extreme but also charming.
Westley is motivated entirely by his love for Buttercup. He explains to her in chapter one that everything he does, he does to please her: "I have taught myself languages because of you. I have made my body strong because I thought you might be pleased by a strong body." Throughout the story, his love-directed motivation encompasses many other ends, and he learns everything the world can teach him, with the sole hope that it might one day prove useful in reclaiming his beloved. Thus, after his tryst with the Dread Pirate Roberts, he returns to Florin about to do everything with a godlike perfection. He can duel better than Inigo. He can wrestle better than Fezzik. He can reason better than Vizzini. He can live through Count Rugen's death machine. He can intimidate the over-confident Prince Humperdinck. In short, he is the ideal man, just as Buttercup is the ideal woman, despite their imperfections.
"Hello, my name is Inigo Montoya; you killed my father; prepare to die." This phrase that Inigo practices repeatedly for his ultimate encounter with Count Rugen completely sums up his motivation throughout the story. We learn in a flashback to his childhood that he had adored his father, a great swordmaker, who had created as his magnum opus a glittering sword for the six- fingered count. The Count returned, was displeased with the product and refused to pay the price he had originally offered, and then in a fit of anger he killed Inigo's father, shattering young Inigo's life. Inigo spends the rest of his childhood and young adulthood mastering the sword, and ultimately becomes a wizard, the highest ranked swordsman in the world. Having achieved this and still not found the Count, he lapsed into depression and alcoholism, and came out of it only when Vizzini recruited him to assist in his criminal organization. He fears losing his purpose again, and therefore he remains faithfully with Vizzini.
Vizzini uses Fezzik, the strongest man alive, for criminal purposes. As an especially large child in Turkey, his parents took him to fight against champions, first locally, then all over the continent. Fezzik hated the sport of fighting but didn't want to lose his parents' affection by refusing. As a matter of fact, it is Fezzik's mother who, when Fezzik protests that fighting will hurt, says the famous words: "Life is pain. Anyone who says different is selling something." Fezzik, although excellent at following instructions, is very bad at remembering them, so Inigo often makes up rhymes that he can repeat to keep Vizzini's rules straight. He is fretful, fair, loyal to Inigo, and an excellent follower, since we are told many times that his only drive in life is not to be left alone.
Prince Humperdinck, the most powerful man in what would one day become Europe, epitomizes everything crotchety, undeserved and dishonest in this story. The country of Florin is his playground, and Buttercup his disposable doll of a wife. While he is an exceptionally talented hunter, he uses his training for his own good: he hunts for sport within his zoo of death, and he disposes of his wife in order to amuse himself with a war. Even under Vizzini's criminal leadership, Fezzik and Inigo use their skills for arguably useful, perhaps even noble purposes, and thus this story is their adventure as it seeps under and around Humperdinck's reign.