Thranduil

[Legolas]

In Lord of the Rings, Appendix B indicates Thranduil founded his kingdom in Mirkwood.

From Appendix B of Lord of the Rings:

In the beginning of this age many of the High Elves still remained. Most of these dwelt in Lindon west of the Ered Luin; but before the building of the Barad-dûr many of the Sindar passed eastward, and some established realms in the forests far away, where their people were mostly Silvan Elves. Thranduil, king in the north of Greenwood the Great, was one of these.

In later writings, presented in the Appendix B of 'Concerning Galadriel and Celeborn' in Unfinished Tales, Oropher, Thranduil's father, is said to have established the elven kingdom and Thranduil came to rule after his father fell in the Last Alliance.

Oropher and Legolas are the only kin of Thranduil noted, so if he is related to Celeborn, we do not know how.

I have taken the time to arrange the Appendix B from Unfinished Tales in html for you to read, so please do by clicking here.

If that does not work, the URL is as follows: http://www.geocities.com/ulmo10/ut-cg-appendixb.html