Absolutely one of my favorite fantasy series (and probably in my top five fantasy series alongside the works of
J.R.R. Tolkien,
C.S. Lewis,
Lewis Carroll, and
J.K. Rowling),
Lloyd Alexander's
The Chronicles of Prydain is a wonderful quintet of books that detail the adventures of Taran and his allies.
The books were published one each year from 1964-1968 and were inspired in part by the epic fantasies of Tolkien and Lewis, but also in part by the Welsh and Celtic mythology found in the
Mabinogian.
Each book follows Taran and his friends as they age and as they challenge the forces of evil represented by the maniacal sorcerer Arawn and his minions.

The books are written in a fairly simple prose style and will primarily appeal to ten to fifteen year old readers, but the characters are so emblematic of the universal archetypes found in myths and fairy tales that they will enchant adult readers too.
The Book of Three tells the story of how Taran, a young Assistant Pig-Keeper at the cottage farm of Caer Dallben, is entrusted with watching over the oracular pig Hen Wen.
When Hen Wen runs away Taran follows her and ends up on his first adventure. Along the way he encounters such figures as the dreaded Horned King, a seductively evil sorceress named Achren, feisty Princess Eilonwy, the legendary warrior Gwydion, the charismatically eccentric bard Fflewddur Fflam, the curmudgeonly dwarf Doli, and the loveable, fury, thieving creature known as Gurgi.
The Black Cauldron is a much darker tale that examines the further adventures of Taran and his friends as they race against the forces of evil to find the mystical Black Cauldron, which possesses the power to create an army of the reanimated dead.
When a group of noble kings and brave warriors arrive at Caer Dallben to discuss plans to find Arawn's Black Cauldron and destroy it forever. The allies, now joined by the egotistical Prince Ellidyr, the Warrior Poet Adaon, the boisterous King Smoit, and the chilly King Morgant, split up into groups on their search. While on their mission Taran learns about sacrifice, honor, and loyalty.
The Castle of Llyr is a fairly light-hearted story in comparison with the others and tells of Princess Eilonwy's heritage and hints at the growing romantic interest between Taran and Eilonwy.
When Eilonwy returns to her ancestral home on the Isle of Mona, Taran and Gurgi escort her, along with her betrothed, the bumbling Prince Rhun. While on the Isle of Mona, Taran is reunited with Fflewddur Fflam and Prince Gwydion and he and his companions must survive the machinations of the evil sorceress Achren, escape from the clutches of a giant, and survive their encounter with a giant mountain cat named Llyan.
Taran Wanderer is perhaps the most moralistic and allegorical of the stories and delves into Taran's past and his search for his true identity.
When Taran realizes his love for Eilonwy and decides that he wishes her hand in marriage he is faced with the dilemma that a Princess cannot marry someone who is not of noble lineage, so Taran goes on a soul-searching journey across Prydain, accompanied only by his crow Kaw and Gurgi, to discover who his parents were. Along the way he meets a villainous band of cutthroats lead by the treacherous Dorath, he stops a war between two feuding kingdoms, he learns the value of hard work in the Free Commots, and is reunited with Fflweddur, Doli, and King Smoit.
The High King stands out as the most epic of the Prydain novels and tells the tale of the final battle against the malevolence of Arawn and his Cauldron-Born.
Taran returns from his journeys abroad and intends to propose to Eilonwy when he learns from his friends Fflewddur and Gwydion that Arawn ambushed them and stole Gwydion's magical sword Arawn which is needed to defeat the evil sorcerer. Taran and his allies make way for the nearby kingdoms and gather forces to stand against Arawn's ever-growing army of the living dead. Along the way, old friends are lost in battle, new enemies are revealed, and Taran realizes the weight of his own destiny as he becomes The High King over all Prydain.
Full of adventure, coming-of-age drama, romance, and tragedy, the books become more sophisticated as they go and have the characters encounter greater and greater dangers as well. What's so fascinating is how Alexander also lets them evolve subtly and how with each book goes he deeper into the foundations of the characters and explores their motivations and their destinies.