Gandalf?
I'm a firestarter, angry firestarter.- Wielder of Fire plus seeing a balrog makes you angry
At gates of doom I saw too soon,- he saw the balrog first
The slaughter and disaster.
White from blue, no minstrel, true.- turned into gandalf the white from grey(Though the books describe his cloak as more blue
Torchbearer and light caster.- makes light with his staff
Ninth in line, renown is mine,- of course he was last to face the balrog
But student beats the master.- he was saruman's student and beats the witchking master of the wraiths?
EDIT: by the by talking via palantir is the reason I never put up Sauron
