Thû, or Sauron...

Lines 2064 to 2110 of the Geste of Beren and Luthien tell of Thû, or as he was known in ‘The Lord of the Rings’, Sauron.  In the Geste, Sauron is a servant of Morgoth, dwelling in his tower on the Wizard’s Isle on the borders of the North where Morgoth dwelt in Angband.

Men called him Thû, and as a god
in after days beneath his rod
bewildered bowed to him, and made
his ghastly temples in the shade.
Not yet by Men enthralled adored,
now was he Morgoth's mightiest lord,
Master of Wolves, whose shivering howl
for ever echoed in the hills, and foul
enchantments and dark sigaldry
did weave and wield. In glamoury
that necromancer held his hosts
of phantoms and of wandering ghosts,
of misbegotten or spell-wronged
monsters that about him thronged,
working his bidding dark and vile:
the werewolves of the Wizard's Isle.
From Thû their coming was not hid;
and though beneath the eaves they slid
of the forest's gloomy-hanging boughs,
he saw them afar, and wolves did rouse:
'Go! fetch me those sneaking Orcs,' he said,
'that fare thus strangely, as if in dread,
and do not come, as all Orcs use
and are commanded, to bring me news
of all their deeds, to me, to Thû.'

From his tower he gazed, and in him grew
suspicion and a brooding thought,
waiting, leering, till they were brought.
Now ringed about with wolves they stand,
and fear their doom. Alas! the land,
the land of Narog left behind!
Foreboding evil weights their mind,
as downcast, halting, they must go
and cross the stony bridge of woe
to Wizard's Isle, and to the throne
there fashioned of blood-darkened stone.
'Where have ye been? What have ye seen?'
'In Elfinesse; and tears and distress,
the fire blowing and the blood flowing,
these have we seen, there have we been.
Thirty we slew and their bodies threw
in a dark pit. The ravens sit
and the owl cries where our swath lies.'
'Come, tell me true, O Morgoth's thralls,
what then in Elfinesse befalls?
What of Nargothrond? Who reigneth there?
Into that realm did your feet dare?’