Imin, Tata, and Enel were the first Elves to awake in the Cuivienyarna. They were called the 'elf-fathers' as they later awoke all the other Elves at the bay of Cuiviénen.
And so it was that the Quendi ever after reckoned in twelves, and that 144 was for long their highest number, so that in none of their later tongues was there any common name for a greater number. And so also it came about that the 'Companions of Imin' or the Eldest Company (of whom came the Vanyar) were nonetheless only fourteen in all, and the smallest company; and the 'Companions of Tata' (of whom came the Noldor) were fifty-six in all; but the 'Companions of Enel' although the Youngest Company were the largest; from them came the Teleri (or Lindar), and they were in the beginning seventy-four in all.
After that, these 3 Elves (and their wives) are never mentioned again. Replacing them as the leaders of the Elves would be: Ingwe, Finwe and Elwe who would become High Kings of each respective Elven race: Vanyar, Noldor and Teleri. (Exception is Elwe, who was replaced by his brother Olwe).
So, why were these 3 first Elves not the ones to lead the Eldar, and why were they never mentioned again?
NOTE: This is not a duplicate of: Are any of the original elves that awoke at Cuiviénen named?