The main characters in The Princess Bride are the princess, initially presented as a rough and untidy beauty named Buttercup—ironically, her father raises cows—and Westley, who is also known as both Farm Boy and the Dread Pirate Roberts.

Buttercup, spoiled by her parents, is allowed to act wildly and often belittles Westley. She calls him foolish and gives orders in a way that suggests she sees herself as royalty even before her engagement to the prince. Eventually, Buttercup realizes she loves Westley. Upon hearing of her affection, Westley confesses his love for her too and decides to travel to America to find a wife. Shortly after his departure, Buttercup receives news that Westley has perished at sea. Despite this, she continues to love him, even as she agrees to marry Prince Humperdinck, a man known for his hunting prowess but lacking genuine interest in Buttercup or love. Buttercup endures a kidnapping, a rescue by the Dread Pirate Roberts—who is actually Westley—a forced marriage to Humperdinck, and another rescue by Westley, who has faced significant trials.

Westley, who has spent most of his life cleaning stables, becomes an unexpected hero. On his journey to America, he is accidentally captured by the Dread Pirate Roberts. Through his admirable conduct, Westley eventually assumes the title of Dread Pirate, as it is traditionally passed from one pirate to another upon retirement. In this role, Westley rescues Buttercup from the clever Sicilian Vizzini and his crew, which includes a giant Turk named Fezzik and a scarred Spaniard, Inigo Montoya. Westley defeats Fezzik and Inigo, outsmarts Vizzini in a cunning game involving poisoned wine, and saves Buttercup. Prince Humperdinck and the six-fingered Count Rugen pursue them, ultimately capturing Buttercup and Westley after they survive the dangerous Fire Swamp.

Buttercup is coerced into marrying the Prince. Meanwhile, Westley is tortured and killed by the count, only to be revived by Fezzik and Inigo, who need a leader after Vizzini's demise. In the end, despite the evil, violence, and suffering, the lovers are reunited, and they live happily ever after (or so it seems).

Each character directly influences the theme by, at some point, obstructing Westley and Buttercup's union. Each becomes a hindrance to their love. Ultimately, they come to accept the truth of Buttercup and Westley's love, and since supporting Westley aligns with their own goals, they help facilitate the lovers' eventual reunion.