Readers first meet Celeborn in Lothlórien, when the Fellowship sought sanctuary in the Golden Woods after the fall of Gandalf. Celeborn was married to the White Lady, Galadriel and together, ruled Lothlorien as Lord and Lady of the Galadhrim.
"Very tall they were, and the Lady no less tall than the Lord; and they were grave and beautiful. They were clad wholly in white; and the hair of the Lady was of deep gold, and the hair of the Lord Celeborn was of silver long and bright; but no sign of age was upon them, unless it were in the depths of their eyes; for these were keen as lances in the starlight, and yet profound, the wells of deep memory." FotR
We don't see much of Celeborn, aside from the advice he offers to the Fellowship. Just who then is Celeborn, called Lord of Lórien and Lord of the Galadhrim?
Celeborn's history is rather fluid as Tolkien passed away before finalizing Galadriel and Celeborn's background. Is Celeborn Teleri, Sindar or even possibly Nandor? Depending on various of Tolkien's writings, both published and unpublished (but noted in the HoME and UT), there are at least three versions of where he came from and who he is.
Celeborn is a grand-nephew of King Thingol (Elwë) of Doriath, although it depends whose grandson he is. The more common variation is that Celeborn is Elmo's grandson; Elmo is the youngest brother of Thingol. In another version, he is Olwë's grandson. In this latter version, Galadriel met Celeborn in Alqualondë and he is a Teleri. In the former version, depending on when Galadriel first met him, Celeborn would either be one of the Sindar--if they met in Doriath--or of the Nandor--if she did not meet him until Lórien. There is still the possibility that Celeborn is Sindar in this third version but he would have left Doriath very early on, and settled in Lorien before the destruction of the Thingol's kingdom.
The following variations on Celeborn's (and Galadriel's) background are condensed and summarized, mostly from The Unfinished Tales.
Celeborn of Lorien - From The Fellowship of the Ring, we learn that "Before the end of the First Age (even before the fall of Nargothrond or Gondolin), Galadriel passed over the mountains and met Celeborn in Lórien."
This implies that Celeborn was either (1) Nandor, departing from the main Teleri host with Lenwe and then leaving to explore further on, eventually settling in Lórien, or (2) Sindar, where he would have left Doriath before it's destruction. The latter is more likely given that his very name is said to be Sindarin and the language did not come into 'existence' until Thingol became King of the Sindar Elves. Celeborn would have had plenty of time between the establishment of Doriath and the coming of the Noldor; Thingol ruled for about 3000-4000 Sun Years (depending on which annal), before any elf returned from Valinor.
Thus, this version would hold true to what Galadriel said in FotR where she first met him in Lórien.
Celeborn of Doriath - Several sources (The Silmarillion, The Road Goes Ever On, and Appendix B of LotR), specifically has it that Celeborn is an "Elf of Doriath". These sources state that Galadriel first met Celeborn in Doriath and they were married in there. Celeborn was the grandson of Elmo, the beloved youngest brother of Elwë (Thingol) and Olwë. Galadriel and Celeborn were thus kin; she was the grand-daughter of Olwë of Alqualondë.
It can be assumed that Celeborn and Galadriel were present at the destruction of Doriath and escaped, very probably leading the survivors away to Sirion. In the Second Age, after the Downfall of Melkor, they left Beleriand and settled for a time in Eriador. There, Amroth and Celebrian were born. (Note: Amroth also had varying backgrounds where he is either the son of Celeborn and Galadriel or the son of Amdir of Lorien.) About II 700-750, they moved eastward and established Eregion, where they ruled.
Sauron, appearing as Annatar, came to Eregion in about II 1200 and eventually caused dissention; Celeborn and Galadriel were thus driven from power. Galadriel left with Celebrian, passing through Moria. However, Celeborn still remembered the dwarves involvement in the Sack of Doriath, refused to have anything to do with the dwarves and remained in Eregion, seemingly powerless.
However, the elves of Eregion finally realized they had been duped; revealed as himself, Sauron the Deceiver attacked Eregion. Celeborn led a sortie out of the city and was able to break through; his forces joined with Elrond's, sent by Gil-galad to relieve the beleaguered city. However, the elven army was unable to pass through Sauron's forces to save Eregion.
After Eregion's downfall and the eventual settlement of Imladris by Elrond, it's assumed that Celeborn remained with Elrond's forces and stayed in Imladris. It was here that Galadriel and Celebrian were reunited with Celeborn. After the final battle of the Last Alliance, where Celeborn and his family settled is debatable as they either dwelt in Belfalas (later Dol Amroth) or in Lindon and just visited Lórien; however, it wasn't until after Amroth was lost that Celeborn and Galadriel took up rule in the Golden Woods.
Celeborn of Aqualondë - In Unfinished Tales, there is a mention of a totally different background for Celeborn where he is Olwë's grandson. Galadriel first met him in Alqualondë as she was dwelling with her mother's people for a while. Here, Celeborn would have been known as Teleporno, which is a Quenya translation of Celeborn. Together, Celeborn and Galadriel had planned on seeking leave of the Valar to sail to Middle-earth when Fëanor's revolt occurred.
They survived the destruction of Alqualondë and were successful in defending Celeborn's ship against destruction. Afterwards, Celeborn and Galadriel fled to Middle-earth, without the Valar's approval, and so fell under the ban of the Noldor. It can be said that there were many reasons that they still sailed: grief for the slayings, desire for retribution, Galadriel's ambition for land of her own, or even need for adventure and exploration.
Celeborn and Galadriel finally arrived at the Grey Havens, where Cirdan ruled the Falas. They were welcomed as kin to King Thingol. They later wedded in Beleriand and the couple departed before the end of the First Age over Ered Lindon (White Mountains). As a Teleri, Celeborn's background contradicts both what has been stated in The Silmarillion and LotR.
Name / Entymology
Celeborn is Sindarin for silver tree or tall tree. There is also a reference to his other name being Teleporno; however, this is the Quenya translation of Celeborn. The name Celeborn is also the Silver Tree, the Tree of Tol Eressea (and later, of Numenor).
celeb = silver (Q = telep, T = kyelep)
orni = tree (Q = orne, Dor. = orn (beech))
orna = tall, uprising
Celeborn's family (Word document)
Notes (from The Silmarillion):
(1) Teleri - the elves who took Olwë as king after Elwë disappeared/fell under enchantment; they eventually arrived in Aman years after the Vanyar and Noldor did. The Teleri settled in Alqualondë.
(2) Sindar - the elves who remained (or were forsaken--the Eglath) in Beleriand and who rejoined Elwë (Thingol) when he woke from his enchantment. The Sindar established Doriath.
(3) Nandor - a group who split from the Teleri host during the journey westward, led by Lenwë. This occurred even before Elwë's disappearance.
The Lord of the Rings
The Lost Roads and Other Writings
Unfinished Tales of Middle-earth and Numenor