It's been almost a decade since Fullmetal Alchemist: Brotherhood came to a end, but it lives on in the hearts of its fans. It's widely cited as one of the best anime of all time and a great place to start if you're interested in the medium.
It's easy to see why it's so popular, with its incredibly animated action sequences and high-stakes plot. But what usually rings most true for viewers is the strength of it's characters. And not just the heroes. FMA:B has a great cast of villains too, and we're counting down the strongest evildoers.
10 Sloth
Sloth doesn't get a lot of screen time and is one of the less interesting homunculi. His primary characteristic is not wanting to do anything, hence his name. Sloth is mostly just a beast of burden more intelligent villains command to perform physical labor or sic on a enemy. He's the largest of the homunculi and is incredibly strong and fast. But, being the personification of the sin of laziness, he isn't compelled to use his power very often. He's also the least intelligent homunculus, claiming that thinking "takes too much effort."
9 Gluttony
As with most of the homunculi in the series, Gluttony possesses enhanced speed and strength, as well as the ability to regenerate his body. Aside from that, his powers are less than impressive. Mostly he can just eat things. His only really impressive ability is being able to open a false Gate of Truth in his stomach, but that only leads to a pocket dimension Ed and Ling were able to break out of. On the negative side, he's pretty dopey and has to be babysat by his siblings, and has "died" more than any other homunculus.
8 Lust
The earliest competent villain to be introduced in the anime, Lust's physical capabilities aren't that much greater than her other siblings. She does possess the Ultimate Spear, which is ability to extend her fingertips into wickedly sharp claws of any length. She manages to hold her own against Roy Mustang for awhile. But Lust isn't a frontline fighter. Instead, she uses her powers of manipulation to slip behind the front lines and lure people to their doom. She manages to seduce many useful people and extract important information before disposing of them.
7 Kimblee
Solf Kimblee is supposedly one of the most powerful alchemists in the series. He's introduced very early as a war criminal imprisoned for acts of cruelty during the Ishvalan civil war. And to be fair, he is a strong fighter and willing to commit extreme violence. His unique brand of alchemy is creating explosions. By using two fundamentally opposed transmutation circles he can destabilize any matter and make it explode, which can be intimidating. But when we see him, his powers are enhanced by a Philosopher's Stone, and he still manages to get beaten down by the main characters over and over again. He seems scary at first, but doesn't rank very high.
6 Envy
Envy might have one of the most powerful unique capabilities in the entire show. They can transform their body to take on the physical characteristics of anything or anyone. This makes them the ideal spy, as they can perfectly replicate the physical appearance and even the voice of other people, and slip into secure areas. They can also transform parts of their body and often does this to make weapons out of their own limbs.
With the right amount of imagination, Envy should be almost unstoppable. Not to mention they possess an incredibly large, powerful monstrous form that boosts their physical power even further. However, Envy doesn't balance their physical prowess with mental strength. They have a very fragile ego and can be goaded and manipulated very easily. They're not the most accomplished fighter and are repeatedly defeated even early in the series.
5 Scar
"The Scarred Man" is one of the most powerful people to go up against the heroes. Before he's recruited to the Elrics' side, he spends his time hunting down and killing State Alchemists as retribution for the atrocities committed during the Ishvalan civil war. He's killed many powerful people, including an alchemist who was supposedly a combat specialist, and has held his own in fights against chimeras and homunculi, as well as against the Elrics themselves. Other than his own combat prowess, he also has an arm tattooed with a transmutation array and can use it to destroy matter. It's only one half of the full array and he can't create like true alchemists, but having his dial permanently set to destruction suits Scar just fine.
4 Wrath
One of only two homunculi created from a human being. He functions as the leader of Amestris, using his identity as King Bradley (yes, his first name is King) to facilitate the villains' nefarious plans. He doesn't possess the immortality or regeneration of the other homunculi, but that doesn't stop him from being extremely powerful. He's a combat specialist with superhuman agility, able to react with extreme precision. He also has the ability Ultimate Eye, which gives him the power to accurately predict his opponents moves before they've taken them. These two taken together means he can attack with perfect efficiency and his enemies are usually beaten before the fight has begun.
3 Pride
Pride is the first homunculus created by Father and one of the most powerful. He poses as a small boy, but this is just a facade since his true body is made up of shadows. He has a few weaknesses, such as only being able to exist within his "container" (which happens to be the entire country) and having his shadow powers rendered useless in complete darkness.
However, the sheer scale of his abilities outweighs this. He can use any shadows anywhere within his container to eavesdrop on their surroundings, and can use shadow tendrils to manipulate and attack anything within range. Pride can also devour and absorb the powers of his prey, so there's no real limit to how strong he can be.
2 Father
The central antagonist of the entire series, Father has existed for hundreds of years. He spent all this time gathering knowledge and power, plotting a way to become God. And he even manages to succeed, becoming a so-called "Perfect Being"—for a little while. His Philosopher's Stone is full of souls, giving him an almost unlimited well of power to draw on, and he's the creator of all the other homunculi. If he's almost as powerful as God, who could be stronger?
1 Greed
The first incarnation of Greed isn't very powerful. He's easily destroyed by Wrath despite his power of Ultimate Shield, which gives him an impenetrable carapace. However, after Greed possesses Ling's body, the two of them learn to work together. Yes, this does give them the best parts of both their skill sets. But this is a shounen anime and we all know what the most powerful force in the universe is: friendship. Greed's bond with Ling shows he's willing to grow and learn. And their team wins. At the end of the day, friendship always triumphs.