Lord Demon by Roger Zelazny; Jane Lindskold

Greatest among the demons was Kai Wren--the Godslayer and Lord Demon--a master swordsman, dreamer, and glassblower who can contain entire universes in bottles of his creation; a legendary warrior who once, long ago, singlehandedly destroyed a god. But now, Kai Wren must seek vengeance for the murder of his devoted human servant, and he fears that this one death heralds the crumbling of a peace that has reigned for a thousand years.

Forced into a series of uncomfortable alliances, Kai Wren strives to preserve the Demon Realms. But his heart has become his fatal weakness, growing soft during years of peace. He has given trust where trust should not be given, only to discover that among his closest companions are those who will betray him--even destroy him--unless he can regain that which once made him LORD DEMON. The great wars between gods and demons began five millennia ago--and ended with the demons' crushing defeat and banishment from their homeland. The demon race would have surely perished in the empty dimension of their exile had they not found a secret conduit to a safe and hidden plane...called Earth.

Greatest among the demons was Kai Wren--the Godslayer and Lord Demon--a master swordsman, dreamer, and glassblower who can contain entire universes in bottles of his creation; a legendary warrior who once, long ago, singlehandedly destroyed a god. But now, Kai Wren must seek vengeance for the murder of his devoted human servant, and he fears that this one death heralds the crumbling of a peace that has reigned for a thousand years.

Forced into a series of uncomfortable alliances, Kai Wren strives to preserve the Demon Realms. But his heart has become his fatal weakness, growing soft during years of peace. He has given trust where trust should not be given, only to discover that among his closest companions are those who will betray him--even destroy him--unless he can regain that which once made him LORD DEMON.