There seems something uniquely suitable about the combination of Dungeons & Dragons and The Lord of the Rings. Whether it's the well-documented inspiration Gygax et al took from Tolkien's works or merely their shared fantasy genre, this is a match made in heaven. One of the most obvious ways to do this as a Dungeon Master is to incorporate elements of the storytelling, lore, imagery, or even setting into a D&D campaign. But for players, the most obvious place to use LotR inspiration is character creation.
Building a character to rival Middle-earth's greatest heroes from the outset obviously isn't possible for the most part thanks to their exceptional skill and prowess. But starting correctly can pave the way for a high-level character that would feel at home in the Third Age. Of all the many characters featured in Tolkien's Legendarium, however, some fit into the D&D 5e rules a bit better than others.
10 King Theoden
Human Banneret Knight
Theoden, King of Rohan is one of the easiest Lord of the Rings characters to translate to D&D. He is undoubtedly a fighter, but picking his subclass is key to making a lore-accurate version of Theoden. As a Bannneret, he would have access to features like Rallying Cry, Bulwark, and Inspiring Surge, all of which fit very well with his role as a battlefield leader of the Rohirrim.
In spite of his heroic death at the hands of the Witch King, Theodin's stats should lean heavily on Constitution and Strength. Additionally, a high Charisma score would make further sense as a representation of what a significant leader of men Theoden was in his own lands. For those who wanted to avoid the potentially unrealistic additional changes picking the Bannere subclass brings with it, he could also play well as a Cavalier thanks to his obvious affinity for riding and horsemanship.
9 Gimli
Dwarf Fighter
Gimli is a fighter in every sense of the word. With a notable focus on strength, the character could work as either a Champion thanks to the Survivor and Remarkable Athlete bonuses, the latter of which is perfectly reflected in his lengthy pursuit of Merry and Pippin with his allies. For those looking for something a little less vanilla, the Battle Master archetype gives a bunch of very Gimli-appropriate combat tricks and maneuvers.
The Great Weapon Fighting feat is also unavoidable, as Gimli's prowess with weapons almost as large as himself is legendary. Skills like Athletics and Intimidation work well, as do Battle Master maneuvers like Sweeping Attack. Gimli should be built as a hill dwarf in order to pack in that little extra HP each level.
8 Sauron
High Elf Warlock or Bard or Fighter/Warlock
Sauron is one of the most powerful and difficult Lord of the Rings characters to adapt to Dungeons & Dragons. Firstly, he comes in two relatively distinct "versions" and he's a member of the demigod-like Maiar alongside Gandalf and Saruman (though he is likely more powerful than both). During the Second Age, Sauron was able to appear in his fair form, and players attempting to replicate this would most likely create a beautiful High Elf with inordinately high Charisma, Perception, Deception and Persuasion. This version of the character would be most at home as a warlock or bard.
After Sauron was revealed, he would take on a far more terrifying form. For this version, he would almost have to multiclass in order to properly represent the extent of his abilities. As well as wielding huge and devastating weapons like a fighter or possibly barbarian, he also has extensive magic that would once again feel most accurate as a warlock. In any case, it would be difficult to show off anything approaching Sauron's powers until the later levels.
7 Legolas
Wood Elf Fighter
Thanks to his woodland background and perceptive nature, it may seem an obvious choice to make Legolas a ranger when starting a new campaign. That said, he is much more at home as a fighter, though totally at odds with the build for his closest ally Gimli. His story gives him several background choices in D&D, with both Noble (thanks to his royal lineage) and Outlander as viable options. Racially, he is a wood elf rather than a high elf and would benefit from bonuses like Keen Senses adding to his perception, all of which fit well with Tolkien's vision for the character.
Acrobatics would be the clearest skill in Legolas's arsenal, something which was only added to in the Peter Jackson adaptations of both The Lord of the Rings and The Hobbit. His stat priority goes all-in on Dexterity and he would be more than capable as both an archer and a two-weapon fighter. Though he would start strong thanks to his class, his attack volume and potency would all increase as he progresses through the levels, further enabling the player to accurately recreate the legendary elf in-game.
6 The Witch King
Human Paladin/Warlock
Tolkien was extremely well respected for his dedication to properly documenting and providing information on all of the major characters in his works. As a result, almost all of them have family trees, full background stories, and demonstrable skills and areas of expertise. The Witch King is not one of those, as his history before becoming Sauron's deadliest servant is shrouded in mystery (beyond being one of the nine men who was given a Ring of Power).
Fortunately, this gives prospective players a little more freedom to represent the character well while still making it their own. In terms of class, paladin is the obvious choice thanks to the heavy armor proficiency, and as a former human, it makes sense to stick with that as a racial choice. His additional magical abilities may also make options like warlock viable, with spells like Fear acting as an appropriate representation of the character's terrifying aura.
5 Elrond
Half-Elf Paladin or Bard
Elrond is one of the most fascinating and omnipresent characters in the entirety of the Legendarium. Though only a half-elf, he becomes one of the most important and influential members of his kin during the Second Age and maintains that throughout the entirety of the Third Age as well. As well as being deeply skilled in both melee and ranged combat, he is a true leader and well-versed in the histories and lore of Middle-earth, perhaps more so than any other.
Depending on what type of representation for this character the player desires, Elrond could work well as either a paladin or a bard. His Intelligence, Charisma, and Wisdom stats would all have to be very high, with perhaps Constitution the stat that suffers the most on a character who has to be so well-rounded.
4 Bilbo Baggins
Halfling Rogue
Of all the hobbits to choose as a character to replicate in D&D, it might at first seem pertinent to choose Frodo or Sam. In actuality Bilbo is the one who has the most transferable and numerous skills. Bilbo is the protagonist of The Hobbit, rather than The Lord of the Rings, and the fate of the dwarven party he accompanied and the Kingdom of Erebor would almost certainly have been different without his aid.
As a lightfoot halfling, Bilbo could be exceptionally mobile and stealthy. Though the Thief rogue subclass may be the obvious choice thanks to his contractual role in the events of The Hobbit, he's more accurately represented in D&D as a Scout rogue instead. The bonuses it grants at higher levels include Superior Mobility and Survivalist, both of which Bilbo demonstrates in spades. His ability to get out of scrapes that would otherwise claim the lives of less perceptive and intelligent characters point towards a build that favors Intelligence and Wisdom more than even Dexterity.
3 Galadriel
High Elf College of Swords Bard
Though depictions of Galadriel in visual media have varied, she is one of Tolkien's most storied and capable characters. Oddly enough, Galadriel would be most accurately represented as a bard, specifically from the College of Swords. As a high elf, she would gain several bonuses to both her primary and secondary abilities and would be a powerful character to pursue in a game of D&D.
Though there is an argument for multiple different backgrounds thanks to Galadriel's long life and uniquely varied contributions to the fight between good and evil, the most effective and accurate would be Haunted One. Her great sense of loss due to the vast numbers of her kin slain first by Morgoth and then Sauron makes this fit well, and the two extra proficiencies it provides would make the immeasurably wise elf a great choice for a new campaign.
2 Gandalf
Bard
The essentially immortal and near-omnipotent Gandalf might not seem a particularly practical option for a D&D build. That said, there are some clear paths that could make a high-level character a pretty close representation of the legendary wizard. The first step could be multiclassing fighter/wizard, since Gandalf is almost as capable with traditional weapons as he is with his magic. But oddly enough, a lot of his abilities and characteristics make him feel at home as a bard.
Thanks to Tolkien's subtle take on magic, there is an ongoing joke in the community that much of what Gandalf can do is possible for 3rd level spellcasters in D&D. His background would definitely be Sage, his knowledge almost unparalleled, and skills such as Arcana, History and Insight (even if he does usually remain as cryptic as possible) all fit his character well. Bard spells are a relatively good fit in their own right but the bard's ability to use spells outside their own tree via Magical Secrets should allow this list to be fleshed out further.
1 Aragorn
Human Ranger
Of all the characters in Lord of the Rings, Aragorn is perhaps the one that fits most clearly into a single class. More specifically, this is the version of Aragorn before he ascended to the throne of Gondor and lived his life in the wilds of the North as the ranger Strider. As a result, building a version of Strider using D&D's take on the ranger makes total sense and works well in terms of the class' skill set, abilities, and stats.
Though Aragorn would have a low starting Charisma stat, building this up would make sense as he becomes who he was born to be. The Outlander background path makes total sense as a reflection of his life after his youth in Rivendell. Skills like Athletics, Animal Handling, and Investigation are perfect, obviously demonstrated by his ability to run indefinitely in pursuit of hobbits, track their path by investigating places they had been, and calm down and communicate with horses.