Arlong the Saw is a sawshark fishman. He was the pirate captain of the all fishman crew, the Arlong Pirates, a former member of the Sun Pirates, and the older brother of Madam Shyarly. He is known for being the main villain in the Arlong Arc and had the highest bounty in East Blue before being defeated by Monkey D. Luffy.
Like many other One Piece characters, he has his own unique laugh, which is "Shahahahaha".
Arlong considers humans to be inferior beings and is very cruel to them. He is keen to separate his race from humans, and is constantly stuck by this mentality that his people are superior to humans in every way. He thinks nothing of killing a town full of humans, although he seems to prefer controlling people with money and deals (like Nami and Nezumi.)
He has an eye for spotting exploitable talent that he can use for his goals and is an excellent planner. He spent eight years using Nami and her maps to plan his takeover of the East Blue. Nevertheless, any promise about money he makes, he keeps. The best example is when his crew urged him to keep Nami even if she brings the 100,000,000 Beli. However, even though Arlong states he can't go back on his word, he has no qualms about exploiting loopholes in his deals to unfairly get his way.
He is rather easy to anger, going berserk after he was attacked by Usopp and having to be dragged back to his base by his crew to prevent him from destroying the whole town. During his fight with Luffy, the boy's constant fighting back made Arlong mad, to the point where it drove him into a deep anger.Arlong himself had expected Luffy to die quickly, but his anger made him become reckless and destructive, even seriously damaging his own HQ building while attacking Luffy.
He has been ill-tempered since his younger years. However, he wasn't always entirely brutal. During a battle with the Marines, Arlong told Jinbe to leave the unconscious Marines alone. However, it was later shown that he had grown more arrogant over time to the point that he completely had no sympathy for humans. Tiger's death led to his hatred hitting rock bottom. He also failed to understand Fisher Tiger's reason for letting humans that they attacked live. As a result, when Arlong led his own crew and had committed murder, humans came to view him as a "monster". He was loathed for the actions of him and his crew. In the end, he enslaved humans just as the humans once enslaved many fishmen.
Though his opinions and his ideals were extreme, he displayed a high level of brotherhood with his crew and even towards Nami despite her species divide. Arlong looked after his crew members and even though he betrayed Nami, he did so because he didn't want to lose her talent. On top of this, in the final moments of the battle with Luffy, he stated that Nami was his crew member and would be forever, and while he never displayed any regard for her as a friend he was prepared to fight to keep her in the crew. If humans insulted their group, Arlong would react to the insult, and due to the high level of concern amongst his officers they would attempt to keep his temper under control. When weaker members of his crew were hurt, Arlong would seek out revenge on those who had committed the act against those crew members.
Ironically, Arlong is a hypocrite, having accused Koala of being raised to look down on fishmen and think of humans as better than everyone else, when Arlong looked down on humans and preached fishmen superiority himself, making him no better than the humans. Surprisingly despite his hatred of humanity according to Hatchan, Arlong would never harm his fellow fishmen no matter the circumstance. He cared for his crew to a level that when Luffy used one of them as a shield, Arlong became extremely angry.