A Darkness at Sethanon(1986)

Raymond E. Feist

Alternate cover edition can be found here

An evil wind blows through Midkemia. Dark legions have risen up to crush the Kingdom of the Isles and enslave it to dire magics. The final battle between Order and Chaos is about to begin in the ruins of the city called Sethanon.

Now Pug, the master magician sometimes known as Milamber, must undertake an awesome and perilous quest to the dawn of time to grapple with an ancient and terrible Enemy for the fate of a thousand worlds.