"I'm listening to the audiobook version of The Prydain Chronicles by Lloyd Alexander. I'm on the third book. I think it's great and exciting and it has deathless warriors in it!"
Stewart Library has these and many other books by Lloyd Alexander;
The Prydain Chronicles:
The Book of Three
The Black Cauldron
The Castle of Llyr
The High King
All published NY: Holt, Rinehart & Winston