High King of the Elves was a title specially reserved for Ingwë who is revered by all Elves and thus is king of all Elves.
The title is comparable to Manwë's title of King of Arda.
History of the Title
The title came into being sometime after the Elves were well established in Aman. As Ingwë was already the appointed King of the Vanyar and as the Vanyar were drawn to Valinor and were close to the Valar, all elves blessed by Manwë hailed him as their most high king.
Ingwë is its one and only titleholder and dwells on Taniquetil next to the throne of Manwë.[1]