Book-Legolas is a vague and cryptic character into whom I've always thought Tolkien put the least thought compared to other characters. That is to be expected since Tolkien had originally meant for Glorfindel to be the Elvish companion of Frodo until he realized Glorfindel is too OP and would slay the Balrog singlehandedly and completely steal the spotlight from Aragorn and Gandalf. So Legolas was a last-minute addition. You don't get to learn anything about him or his past. He is rather one-dimensional. Tolkien even cheated Legolas out of a background by making him related to the nameless Elvenking in The Hobbit so he wouldn't have to explain his past. We learn more about Gimli than we ever do about Legolas which is odd because normally, Tolkien kept his Dwarves a mystique while he couldn't get quiet about his precious Elves. We don't know about Legolas's relationship with his dad, or his doings before the quest, his age, his accomplishments, etc. I kinda feel sorry for this fictional character, the poor thing was neglected by his own creator.
Book-Legolas does not have much of personality outside of cracking jokes once in a while (mostly in the first book, very little in the other two books) and being less prejudiced toward Gimli than Gimli is towards him. Even when his sea-longing is awakened and he is to never find peace in Middle-Earth again, he is still his old self, with no change at all. Merry and Pippin were more devastated about Legolas’s sea-longing than Legolas himself. Weird.
His friendship with Gimli is kinda there but it's not as grand or intimate as the movies may lead you to believe. Even after Lórien and meeting Galadriel, Gimli could still be a jerk to Legolas. He called the Elf "a fool" for his dislike and fear of Helm's Deep and the caves beneath it; but Legolas is as always gracious enough to ignore Gimli's condescending behaviour. They never seem particularly close in the narrative, even when their promise about visiting Fangorn and Glittering Caves after the war seemed to have been made out of irritation and rivalry. Their legendary friendship is hinted to have truly started during their travels to Fangorn and Glittering Caves after the War of the Ring.
Another part of his character is his loyalty and undying love toward Aragorn. Legolas gives eulogies and speeches about Aragorn's awesomeness and might and coolness frequently. Legolas is a fangirl!
When Legolas and Gimli arrive at Minas Tirith, both mark that it's kind of an ugly city. Gimli says "…when Aragorn comes into his own" he would bring Dwarfish stonewrights to fix the poor architecture of Minas Tirith. Legolas says that "If Aragorn comes into his own" he would bring Woodland Elves to make the city beautiful. I found it an amusing contrast. Gimli seems to be more hopeful than Legolas. Or perhaps I look too deep into that part because later, when Aragorn reveals to Legolas and Gimli that he has touched the Palantir, Legolas remains calm and trustful of Aragorn's choice while Gimli is angered and concerned that Aragorn might have given something away to Sauron; Aragorn is quite offended that Gimli would think that way.
Legolas lovingly follows Aragorn to Black Gate of Mordor where two-thirds of his people were slaughtered 3000 years ago. If you hoped that last part was mentioned in the books or it has an effect on Legolas's decision, you're about to be disappointed. The tragedy of Woodland Elves is never mentioned in Lord of the Rings books.
While it's never really directly stated, Legolas's hinted to be well-educated among his kind: he understands Sindarin in Lórien dialect well enough, and he also knows Silvan and Westron tongues. The last one is a big deal because few Elves in Lórien understood Westron, and they are supposed to be some of the wisest elves around (or so Galadriel says). So Legolas is wiser than them. He also knows history as he sings songs and gives long-ass history lessons for the Fellowship (those are in fact for the readers *winks*) about all kinds of things from Amroth and Nimrodel to Lórien to line of Lúthien and everyone else comically ignores him and his emotional, poetic lectures.
Interestingly, it’s Legolas who first realizes that Durin’s Bane is a Balrog and not even Gandalf knows what it was at first. Even Aragorn doesn’t seem to understand it since when he tries to explain to Galadriel and Celeborn what happened in Moria, he blanks out when he gets to the Balrog part and simply calls it “An evil of Ancient World” and it’s Legolas who explains that it was a Balrog.
But there is a weird inconsistency: He doesn't seem know much about Eregion. Or perhaps Tolkien himself hadn't decided on the exact history of Eregion since Gandalf doesn't make comment on that land either. Legolas says Eregion Elves have sailed West while in Tolkien's notes, different accounts have been given about the fate of those Elves. I find it weird that a Sindarin prince would be so ignorant about Eregion. I think Tolkien would have changed this part, had he gotten to revise the books.
The way Legolas talks about Lórien with so much passion and how beautiful that wood looks in the spring (he also laments that they are going there in wintertime) and also the fact he immediately recognises Nimrodel River suggests he has seen the Golden Wood at least once. The way he dances over the secret power that protects the woods shows he doesn't want to discuss Galadriel (and perhaps her ring too) in Gimli's presence whom he distrusted. Haldir believes Legolas should answer for any mischief or trouble Boromir and Gimli might cause. Legolas also believes himself to be a "kinsman" in Lórien which should grant him the rights to wander in the woods without blindfold. He seems to be known in the Golden Wood.
But he also says he hadn't climbed a Mallorn (golden tree) before, and that it has been a while since a Mirkwood elf has ventured there. This could mean Legolas himself hadn't been to Lórien before but I believe it means it has been a long time since Legolas himself has visited Lórien. Perhaps Mallorn weren’t as common last time Legolas visited. It's kind of vague just like Legolas himself.
In Return of the King, when the Grey Company arrives, Legolas explains to Merry, Pippin and Gimli that not everyone in the company is a ranger and the two in "less sombre gears" are sons of Elrond. That means he is familiar with Elladan and Elrohir. Legolas also knows that Song of Nimrodel and Amroth is sung in Westron in Rivendell and he also remembers some verses of it, so he is familiar with Imladris and its inhabitants and he has been there before Elrond’s Council.
All in all, it can be inferred that Book-Legolas is knowledgeable and familiar with Rivendell and Lórien and seems somewhat wordly. Otherwise Elrond and Thranduil would sound super irresponsible. I cannot imagine Thranduil sending his son as a messenger to a place he hasn't been to before or Elrond sending an inexperienced elf on such a perilous journey to protect the Hobbits.
As for his looks, he is described as "tall" and "lithe" and "fair of face beyond the measure of Men" to the point men and women gawk at him.
His hair colour and his eye colour are left unmentioned, though some fans consider this part of the book as an indication that he had dark hair: "Frodo looked up at the Elf standing tall above him, as he gazed into the night, seeking a mark to shoot at. His head was dark, crowned with sharp white stars that glittered in the black pools of the sky behind."
However everything was pitch-black at the time, and Legolas couldn't see what it was that he shot and his eyes are better than Frodo's. Frodo saw Legolas like a dark silhouette in the faint light of the stars. He could be blond, dark-haired, silver-haired, even red-haired, though I find the last one very unlikely.
Kinda odd that the most significant elf character's looks are not described.
When it comes to strength, Legolas is a formidable warrior even if Tolkien's subtle writing style didn't show it. Legolas was handpicked by Lord Elrond as the Elvish companion of Frodo which means he has to be particularly powerful among his peers, not Glorfindel league but still strong. Certainly stronger than the many Noldorin elves in Imladris including Elrond's own sons over whom Elrond chose Legolas. He can shoot down Nazgûls, and he was strong enough to come out of all the battles and skirmishes unscathed.
Tolkien's subtle style wasn't about describing the characters' strength in battle (except Aragorn's because he is 'awesome' and Tolkien wants you to remember that always). However he gave us a little bit of each of the Fellowship fighter’s prowess, but he kinda neglected Legolas as always. That, along with the emphasis the books put on Legolas's beauty and grace and his singing and his poetic language gave some readers the impression that Legolas's a bit of a lightweight. According to Christopher Tolkien, such interpretations angered his father, who had to set things straight with the readers in one of his letters; the Elf of Fellowship is not a wimp:
"He was tall as a young tree, lithe, immensely strong, able swiftly to draw a great war-bow and shoot down a Nazgûl, endowed with the tremendous vitality of Elvish bodies, so hard and resistant to hurt that he went only in light shoes over rock or through snow, the most tireless of all the Fellowship"
So don't imagine Legolas was "ladylike" or weak.
Maybe such interpretations were the result of Tolkien's own neglect of Legolas's character. Perhaps Tolkien wasn't that good at selling Legolas as an Elf. Why else would he have to write that letter?
That's all there is about Book-Legolas , I guess. There are a few things we learn about him in the appendices but I don't think it is fair to bring them up here because the films couldn't adapt those; I will talk about them nonetheless: After the war, Legolas resists the sea to be with his mortal friends. He traveled to Glittering Caves and Fangorn with Gimli (and possibly Merry and Pippin accompanied them since it was Gimli's wish to show the Hobbits the Glittering Caves). He also brought a colony of Elves down to Itihlien and made it the fairest country in all Middle-Earth; Legolas must possess some leadership abilities in addition to the wisdom to revitalize a damaged realm such as Ithilien. He kept his word regarding the beautification of Minas Tirith. It's only after the death of his beloved Aragorn that he gives in to the sea and Gimli goes with him for the love of Galadriel.
The movies I believe did the character justice and some more. His relationship with his dad and his past are shown in The Hobbit movies but it's not fair to add those to this post since Legolas was not in TH book.
Like in the books, Legolas is less prejudiced toward Gimli, however he can be a tad racist at times. He looks visibly annoyed when Gimli joins the Fellowship. When Gandalf says even the Dwarves could not find where they placed their secret doors, Legolas says "Why doesn't that surprise me?"
He has a sense of humour and cracks jokes once in a while like teasing Gimli in Helm's Deep and counting their kills (as it happened in the books). He is humourous consistently through all three films. Like in the books, he loses to Gimli by one orc.
He also gives history lessons, mainly about Path of the Dead and Fangorn forest.
Legolas is not shown to be singing apart from the magnificent "They're taking the Hobbits to the Isengard!". A shame that he didn't sing more. Orlando Bloom is a gifted singer.
Like in the books, he tells Galadriel and Celeborn about the Balrog. Legolas looks honoured when he remembers receiving a bow of Galadhrim from the Lady Galadriel. He has great respect for the Lady of the Woods.
Legolas is fiercely protective of and loyal to Gimli and Aragorn; I believe his friendships with both of them were more fleshed out in the movies. When Legolas learns about Galadriel's gift to Gimli, he looks genuinely happy for his friend:
This scene is so wholesome and while it wasn't in the book, I can totally see Book-Legolas being this happy for his friend too. I wish Book-Legolas had some wholesome moments.
There is also this beautiful dialogue in Return of the King that wasn't in the books:
Legolas also loves Aragorn deeply. He jumps to his defense in Elrond's Council like a supportive BFF. He is also shown to be very protective of Aragorn like in Moria and in the final battle at the Black Gate. Both he and Gimli look devastated when they realize Aragorn might have died in his fall. Legolas kept the Evenstar necklace for Aragorn when he fell of the cliff hoping that his friend still lived. He greets Aragorn in Helm’s Deep.
Legolas also kinda gave away Arwen in her wedding. All these imply a strong relationship with Elrond's family.
While Elladan and Elrohir do exist in the movies (they are sitting in either sides of Elrond in the Council), it seems Movie-Legolas's role and character amalgamates some of those brothers' roles with Book-Legolas. It was a good idea, imo. Two useless characters' roles are shortened while more is added to a relevant character and a member of Fellowship.
I think the one noticeable difference between the films and books is that Movie-Legolas isn't always as positive as Book-Legolas; he can feel doubt and despair like in Helm's Deep when the odds were against Theoden, and Legolas tried to convince Aragorn to save himself from a losing battle. Later, he realized his mistake and apologized to his friend.
According to the movie guide books and Orlando Bloom, Legolas is 2931 years old. Bloom says Legolas has seen the world and is experienced; but Gandalf's death is the first time he loses a dear 'mortal' friend (remember that Legolas, like most others, thinks Gandalf is mortal) and he's both perplexed and saddened by the loss; he doesn't understand where Gandalf has gone and is visibly confused and grieved:
(By the way, I think this is the only time Legolas looks dirty and unclean)
And in his confusion and grief, he is asked by Aragorn to pick up the Hobbits. Aragorn asks him first like he expects Legolas to get over it faster than others. And he does after some hesitation. He helps Merry and Pippin up.
But as he says in Lorien, he is not yet over it:
Legolas reacts to Boromir's death similarly too; a mix of grief and confusion:
Movie-Legolas has a subtle arc and it is about coming to terms with death, getting over despair and trusting his king and friend, Aragorn.
He has been given golden hair (which looks more silver-blond at times than the radiant golden hair of Galadriel) as his father's hair was described in The Hobbit book.
As for his strength, it's not far-fetched to think Book-Legolas can do all the impressive stuff Legolas does in LotR movies. If Movie-Legolas can kill a Mûmak, Book-Legolas can shoot down a Ringwraith. The latter feat is way more impressive, in my opinion. I don't get why some book fans were pissed off about Legolas's feats of strength in LotR films. None of them looked bad. Tolkien elves had done crazier things.
(However I thought his feats looked ridiculous in The Hobbits: Battle of Five Armies as did most of the actions in that movie but let’s not get into that.)
All in all an accurate adaptation of the character but Movie-Legolas is more fleshed out and less underwritten and has some dimensionality and a tad more personality than Book-Legolas. I would have loved to see more of Movie-Legolas. Peter Jackson did an impressive job of handling the character considering the runtime constraint and the moderate pressure the studios put on him. Orlando Bloom was a really good casting choice, imo. He really captured Legolas's weirdness well.