An Ithiriel, simply put, is a supreme ruler of all elvenkind--one who is elevated above kinship or kingdom as the highest authority. In this regard it is not entirely dissimilar from an emperor or high king. Throughout most of recorded time, this office has lain vacant.
In the world's earliest days, there were no separate realms among the elves, and the title of Ithiriel was a hereditary one, passing from Shalath Serannar to his son Laenor. Some ten thousand years ago, this unity broke down, and the elves spread apart, the title of Ithiriel falling into long millennia of disuse.
Only much later, six hundred years before the coming of the Host and the exodus of the elves, would a new Ithiriel be named. Elexia Marindur was able to bring together the elven peoples in the name of healing the scars and wounds of their many conflicts among themselves. She achieved this through force of charisma and canny diplomacy.
However, many elves distrust and hate the idea of a single ruler above them all, believing it will bring about the end of the unique cultures and ways of life of their individual kinships. At one time, a secret group of elves formed a society known as the Harbingers to ensure no Ithiriel would rule--and as punishment, they were slain, their very souls Reaped out of existence.
The Ithiriel Elexia perished along with the greater part of elvenkind on the journey to the Immortal Lands, sank beneath the waves in a terrible and unexpected storm at sea.
Currently, the office of Ithiriel is vacant. Whether or not it should be filled anew is a source of considerable controversy.