Greed is a common theme in The Lord of the Rings, with the greed of Men making them desire the One Ring and the greed of Dwarves causing them to dig too deep into Moria. And while this desire for riches and gold usually ends in tragedy, some lived prosperous lives with more wealth than most can imagine, becoming Middle-earth's very first billionaires.
Of course, measuring wealth in a fantasy setting can be difficult; not only is everything measured in gold but magical items have to be factored in as well. It could easily be argued that Galadriel was the richest of them all because she both ruled over Lothlórien forest and held a huge number of magical trinkets. From the Phial of Galadriel to the Mirror of Galadriel, all these one-of-a-kind items that were sought after by many could be marked as priceless. That said, there are a few people from The Lord of the Rings and beyond who may have had Galadriel beat.
Who Owned the Most Gold in The Lord of the Rings?
From a purely monetary value, Frodo was actually the richest of all the Fellowship, as his Mithril shirt's worth "was greater than the value of the whole Shire and everything in it." This stems from the extreme rarity of Mithril. It's emphasized time and time again in The Lord of the Rings just how expensive it really is, with the entire mines of Moria dedicated to this one rare material. And so, whoever owns the most Mithril is likely the wealthiest in Middle-earth.
Without a doubt, it would be the Dwarves who possess the largest quantity of Mithril; they were the ones who mined it, and Dwarves have always been renowned for their greed and treasure hoards. Although, at the time of The Lord of the Rings, no one holds ownership over Moria. This leaves the Dwarves of Erebor as the wealthiest in the world -- more specifically, Dáin II Ironfoot.
How Much Erebor's Dwarves Were Worth
At the time of The Hobbit, Dáin was Lord of the Iron Hills and one of the few Dwarf leaders in Middle-earth. So after Thorin Oakenshield died in battle, it was Dáin who became King under the Mountain. Not only did he rule over two huge pieces of land, but he also inherited the entire wealth of Erebor and later reopened the Mines so that trade could resume once more. So his treasure hoard was likely the largest in all Middle-earth.
When Smaug the Dragon sat upon Erebor's wealth, it's estimated that his worth was around $54.1 billion (when converted into real-life values). And while much of this was put towards rebuilding the Men of Laketown, that still left Dáin with billions of gold to spare and an entire mine back in commission. On top of that, it's unknown how much Mithril the Dwarves actually owned, but it's safe to say that Frodo's shirt wasn't the only one.
So while some in Middle-earth may have riches through power and artifacts, none can top the wealth of Dwarves. And they likely became even wealthier after The Lord of the Rings, with it being prophesied that the Dwarves would one day return to Khazad-dûm and reopen the vast mines of Moria.