First of all, I’d just like to make the point that Thranduil is, unfortunately, not a very well expounded-upon character. He was very important in the grand scheme of things and in the course of history however he generally played a rather minor role in the important events (as compared to characters such as Gil-galad, Elendil and Isildur, and even Celeborn). Truly, the only time his name specifically comes into the annals of Middle-earth apart from tagged with another name is in the Third Age, specifically the Battle of Five Armies and the Quest for Erebor.
Let’s start with the basics though, shall we? Where he was born, his parentage, his childhood, who he married, his children, etc.; the basic facts that make up Thranduil’s social dynamic, and set the stage for the political importance that would follow.
Thranduil was most likely born in Doriath during the First Age to Oropher and an unnamed mother. Now, Doriath was the great woodland kingdom ruled by Elu Thingol, which spanned from before the rising of the Sun and Moon, until ~506 of the First Age. Now, Oropher’s relationship to Thingol is unknown, however it is believed by many (myself included) that Oropher was likely a lord of Doriath, as he has some importance in the following years, even before he settles in the Greenwood and is chosen as king there. Thus it is also likely that Oropher was (very distantly) related to Thingol. This provides some very intriguing potential familial relationships, however I shan’t explore those here.
Of course, Thranduil did not live long in Doriath, for it was sacked (more than once). Eventually, Thranduil and his father left the area, instead moving down toward another forest with a small group of other Sinda (the “greater” of the Woodelven kindreds, the other being the Silvan). The forest that they took up residence in was known as Greenwood, and it was populated by the Silvan Elves. Although I will talk more of this time period and the politics regarding this transition in the next essay, suffice it to say now that Oropher was chosen to be the king of the newly formed kingdom, and thus Thranduil was now a prince.
It is not known when Thranduil took a wife. Most likely it was some time during the Second Age, and most likely it was one of the Silvan Elves of Greenwood. However, it is not actually known for certain. Indeed, she could have been a refugee of Gondolin, or a child of the Second Age born in Lindon. All that we do know for certain is that he did indeed take a wife, for some time in the Third Age, a son was born to them.
It actually is not known for absolute certainty when Legolas was born…I suppose it was possible that he was born in the Second Age. However, truth be told, I find it highly unlikely. This is in regards to a certain line in The Fellowship of the Ring, in which it states clearly that Legolas appeared young and unworn by the cares and woes of the world as many of the Elves were. Simply put, Legolas was still considered young, and without much of the sorrow that the older Elves bore. If Legolas had been alive for the War of the Last Alliance, I personally find it doubtful that he would still be so young-hearted and unjaded.
You’re probably beginning to get tired of hearing this, but…it’s not known just how many children Thranduil and his wife had. Legolas is the only known child, however there is the very real possibility that they had two (or so) more children, either son or daughter. Elven families were small as a general rule, so it is doubtful that Legolas has four brothers and two sisters, or even really three more siblings. However, as it is never stated, it is up to the reader (or writer) to determine all of the family dynamics when it comes to Thranduil. In fact, the same goes for Thranduil’s own siblings. Again, no other child (or in Thranduil’s case sibling) was ever mentioned, however that does not completely eradicate the possibility of his having siblings.
And now we come to another tricky topic in Thranduil’s life: what happened to his wife. You guessed it…we don’t really know. There are many theories, the most prevalent being that she is either dead or sailed as we hear absolutely nothing of her. A slightly more uncommon idea (although most certainly not absent) is the belief that she is still in Middle-earth. She just never comes up in conversation. In fact, it’s quite possible that she wouldn’t have ever been mentioned – Celebrían, literally one of the Elves of greatest lineage in the Third Age (ironically trumped only by her husband, and even that is debatable), married to one of the three Ringbearers, mother of Arwen Undómiel and Elladan and Elrohir Elrondion, former Lady of Imladris, is only mentioned in passing twice in The Lord of the Rings: Aragorn mentions her name and the fact that she is Arwen’s mother, and an explanation as to why Elladan and Elrohir hate Orcs. Granted, she is sailed so she is not present, but despite her great importance in the shaping and ordering of the Third Age, she is hardly even mentioned. Legolas’s mother, even if she was alive, likely would not have come up, as they never passed through Mirkwood, and Legolas’s discussion never truly turned to his home or family. And as for The Hobbit; well, what reason would there be for any of the Dwarves to have seen her, and even if Bilbo had seen her, how could he have known who she was?
All of that lengthy paragraph to say: no one knows what happened to Thranduil’s wife. There is evidence to support that she is likely no longer present…but then there is also evidence to suggest that the evidence that supported it isn’t evidence at all.
Truthfully, when it all comes down to it, this area of Thranduil’s character is very much open for debate and headcanon. All that is really known is
a) Thranduil was born in the First Age to Oropher
b) Thranduil, as the son of Oropher, was the prince (and after Oropher died the king) of Greenwood (which would become Mirkwood)
c) Thranduil was married
d) Thranduil had at least one son named Legolas
And that’s it. So all of the rest of the details really can be added in, per each reader (or writer)’s discretion and choice.