Nerdanel
Married to the greatest - wife of Fëanor, allegedly greates elf in history
the only one he would listen to - self-explanatory
Gave birth to the Fair - mother of Celegorm the fair
and to the proudest - mother of Caranthir the dark
and the one who was uniting - Maedhros who formed Union of, yes, again Maedhros
Fate is unknown...