Princess Eilonwy

Eilonwy is introduced in The Book of Three. The companions are captured and taken to Spiral Castle, the stronghold of Achren, the former queen of all Prydain and mentor to Arawn, who later overthrew Achren and sent her into exile. At first, Eilonwy seems to be only a rather talkative, easily distracted girl, but she rescues Taran and Fflewddur Fflam (the latter by mistake, since Taran thought the only other person in the dungeons would be Gwydion, his companion, and asked Eilonwy to rescue the other person she described to him). She is described as being perhaps one or two years younger than Taran, the protagonist of the series, but Taran's own age is never given so we have no definite idea of how old either of the characters are.

On their way out of the castle, they pass through a maze of underground passages and eventually reach a tomb where Eilonwy retrieves a sword. This sword is Dyrnwyn, a magical sword with a blade that bursts into flame when it is drawn. However, Eilonwy will not allow Taran to examine the sword or draw it from its rune-inscribed scabbard; despite her incomplete magical training, she is knowledgeable enough to recognize that the sword is highly magical and best left to experts.

Following the destruction of Spiral Castle, Eilonwy joins Taran, Fflewddur, and Gurgi on their journey to warn the Sons of Don of an advancing attack (though Taran asked Fflewddur to take her back to her own kinsmen, she refused to the point of threatening to break Fflewddur's harp over his head if he tried). She attempts to halt several Cauldron Born at one point with an enchanted arrow, but it does not work as she intended. When they are captured by the Fair Folk, she convinces the king to give them Hen Wen, provisions, and a guide to Caer Dathyl. Eilonwy also agrees with Taran's decision to rescue an injured young gwythaint. When the group must pass through a valley with the Horned King's war band, Eilonwy rides with Taran and leaps at the Horned King to try to protect him. When Taran wakes up in Caer Dathyl, she tells him what happened and helps him recover.

Throughout the book, Taran presumes Eilonwy to be, apart from her enchanted heritage, an ordinary girl, and she makes no effort to contradict the presumption. At the end of the story, however, it is revealed to him that she is, in fact, a royal princess, and she is invited to make her home in Caer Dallben.

After the events in The Book of Three, Eilonwy comes to live at Caer Dallben, home of Dallben the enchanter and Taran. She accompanies Taran on many of his later adventures, and her courage and determination never falter. We later discover that she is the last living descendant of Llyr Half-Speech, the Sea King, which is why Achren abducted the girl as a small child. She is the only one capable of reading a tome that requires the light of her bauble, which only Eilonwy can cause to light. Because her magical tutoring under Queen Achren was incomplete, her ability to perform magic is severely hindered, though she retains and displays certain inborn abilities throughout the series.

Physically, Eilonwy is described as blue-eyed, with red-gold hair (though the film The Black Cauldron depicts her as a blonde). She has a good heart, but is very determined to have her own way and quarrels frequently with Taran, although the quarrels do not last long. She is never without her "bauble" – a magical ball that she can make give off light, which sometimes shows things not visible under ordinary lights. The Castle of Llyr, the third novel in the series, reveals that this is really the Golden Pelydryn, a magical artifact passed through Eilonwy's family from mother to daughter. The events of that book bring Eilonwy back to her ancestral home, Caer Colur, and give her a greater sense of her ancestry. The Disney film depicts the bauble as a semi-sentient object that floats through the air under its own power, but in the books, it is described more like an orb of gold that must be carried.

The fourth book in the series, Taran Wanderer, sheds light on the ultimate fate of Eilonwy's mother, Princess Angharad. Eilonwy herself never appears in this book, though she is referenced at various times. Taran makes this discovery while Eilonwy is being fostered at the foreign court of King Rhuddlum and Queen Teleria, learning to be 'a proper princess'. Whether he ever shared the information with Eilonwy is uncertain, though it seems likely that he refrained from doing so in an effort to spare her anguish. By this time Taran realizes that he's fallen in love with Eilonwy, but he is reluctant to act on it because, having been raised as a commoner while Eilonwy is a royal princess, Taran feels that he really does not belong in her world. On the other hand, Eilonwy herself seems to have grown rather fond of Taran by this point, even if she will not admit it.

Taran and Eilonwy's feelings for one another are much more evident throughout the 5th and final book of the Prydain Chronicles, The High King. Although these feelings are never spoken of directly until the last few pages of the novel, Taran and Eilonwy's interactions with one another are noticeably different than in the previous books. Taran internally pines for Eilonwy, and fears for her safety in the midst of the escalating war. Eilonwy's change towards Taran is far more subtle, yet no less certain, and is experienced perhaps more gradually over the course of the entire series in contrast with Taran's very abrupt realization of his feelings towards the Princess in the first chapter of book three, The Castle of Llyr. At the end of The High King, Taran becomes High King of Prydain and marries Eilonwy. She must, however, renounce her magical powers to be allowed to stay in Prydain, since all magical folk are leaving for the Summer Country. The series comes to its conclusion as the coronation and marriage of King Taran and Queen Eilonwy are announced to the people.

A sixth book was published in the series, The Foundling and Other Tales from Prydain. Among the stories included therein, readers learn about the circumstances that resulted in Princess Angharad running away from home to marry the commoner Geraint. Although Eilonwy inherited her mother's red-gold hair and magical heritage, her intense blue eyes came from her father.