The One Piece universe has many benevolent leaders that only seek the best for their people. Neptune and Cobra are both great examples, as they were willing to put aside preconceptions about pirates in order to save their kingdoms.
However, there are just as many villainous tyrants who oppress those beneath them. Such monsters have clearly defined themselves as enemies of freedom, many of whom have been personally responsible for the series' worst travesties. The brutality of these dictators is legendary across the high seas, and not all of them have been taken down yet.
10 Wapol Tried To Horde Drum Kingdom's Doctors
Wapol was Drum Kingdom's original leader and one of the most sinister villains in the series. In order to procure his subjects' loyalty, he hoarded a handful of doctors and banished the rest from his nation.
Those who refused were hunted down and either killed or forced into exile. This made Chopper's backstory especially traumatic, as his mentor refused to stop helping those who needed him most. Fortunately, Kureha proved far more elusive in spite of her age and even took up residence in Wapol's old castle.
9 Akainu Was An Oppressive Fleet Admiral
Akainu was hand-picked by the Five Elders in order to serve as the World Government's next fleet admiral. He was as brutal toward pirates as he was his own soldiers. During the battle for Marineford, he killed a man who sought to retreat from Whitebeard's forces.
Akainu had no sense of honor, as seen when he manipulated Squard into betraying his friends and "father." As fleet admiral, Akainu has managed to temper his pugnacious disposition and allocate Marine resources to territories that they can successfully overwhelm. His newfound restraint renders him even more terrifying.
8 Orochi Oppressed Wano For Decades
Hunted as a child, Orochi dedicated his entire life to avenging the Kurozumi Clan. To this end, he manipulated the people of Wano into becoming its next shogun and reigned oppressively ever since.
Orochi wasn't simply misguided when abusing the people of Wano; he actively relished their suffering and did what he could to exacerbate it. In his mind, every starving child or poison-choked river corrected a slight that had been dealt against him. However, he overestimated his trust in Kaido, which nearly resulted in the destruction of the Flower Capital.
7 Charloss Embodied The Worst Of The Celestial Dragons
The Celestial Dragons were already notorious for their sense of entitlement. However, Charloss was by far the worst among them, especially due to his wanton misappropriation of Marine resources to slake his own ego.
Although seldom appearing in the series, Charloss tried to buy Camie on the black market, caused the Sabaody incident, and nearly ignited a global conflict between humans and fishmen at the Reverie. He did not care for anything but himself and seldom considered the ramifications of his crimes. Worse yet, Charloss hadn't earned any of the luxuries he enjoyed.
6 Doflamingo Turned Dressrosa Into A Crime Syndicate
Doflamingo usurped Dressrosa by intimidating King Riku and turning the public against him. Although transforming the country into a prosperous metropolis, its corruption made it virtually unlivable. Many subjects went missing in the middle of the night, having been changed into toy slaves for an illegal Devil Fruit operation.
In the end, Doflamingo did not care for his people whatsoever. He attempted to massacre them in a giant birdcage at the conclusion of the arc, which would have killed members of his own crew in the process.
5 Big Mom Destroyed Her Own Country On A Whim
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Despite propagating values like equality and peace, Big Mom was extremely corrupt. She attempted to betray Germa 66 in order to steal their technology, resulting in a conflict between the two kingdoms.
Additionally, Big Mom was oppressive to the subjects of Whole Cake Island and even her own crew. During her hunger pangs, she didn't care about the homes destroyed or lives lost so long as her appetite was sated. Additionally, she demanded portions of her people's lives just so that they could continue living in the country.
4 Arlong Enslaved A Local Village & Exploited Nami's Gullibility
After attacking a village and crushing its few protectors, Arlong proclaimed himself as the new leader. Since he had connections in the Marines, they refused to help, effectively making his victims slaves.
Arlong offered Nami the chance to "buy" her people's freedom in exchange for a large amount of money. However, even after she gathered it, he had the Marines confiscate it from her. Were it not for Luffy, Arlong would have expected Nami to serve him until she died broken and alone.
3 Eneru Acted Like A God To The People Of Skypiea
After usurping Gan Fall, Eneru became the new leader of Skypiea. He forced the previous ruler's servants to construct a great arc and made his subjects worship him like a god. Those who refused were punished with lightning, which quickly established a precedent.
Eneru's desire for praise was superficial. In reality, he coveted a massive golden bell for its splendor and craftsmanship. After finding it, he intended to destroy Skypiea since it no longer served a purpose to him.
2 Kaido Was The Brutal Emperor Of The Beast Pirates
A legend among pirates and Marines everywhere, Kaido was deemed the strongest living creature in the world. He ruled Wano for roughly two decades, suppressing the spirits of its people and forcing any remaining opposition to work in the slave pits of Udon.
Kaido was mostly apathetic toward the lives of his own subordinates. He didn't care that Queen turned them into ice oni and offered the Tobi Roppo a chance to replace the lead performers if they routed the Straw Hats. Ultimately, Kaido's only goal is to obtain a death as glorious and violent as Whitebeard's.
1 Im Was The World Government's Clandestine Ruler
Im was the true leader of the World Government. They held an office so prestigious that the Five Elders bowed down in subordination. Moreover, given their interest in erasing Ohara, it's almost certain that they played a role in the Void Century.
What makes Im particularly treacherous is their wish to remain anonymous. It protects them from being held accountable for the World Government's worst atrocities and suggests that if they are exposed, it might spell political disaster. As the series reaches the final saga, their confrontation with Luffy will be particularly cinematic.