Thranduil, while a king, was a king of Silvan Elves, a group of Elves that gave up the journey to Valinor quite early. Although they were Nandor (and therfore Teleri) in origin. In terms of the grandeur of the Elves, Thranduil was a far less important Elf-lord(/Lady) in comparison to the other three. More @Wikipedia
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