Meruem is the king of the Chimera Ants, an extremely dangerous insect species that can evolve by having their queen devour other species and giving the ants it gives birth to their traits. Meruem was born prematurely by ripping his way out of the queen's body, fully-grown, killing her in the process. At first, Meruem was a cruel and violent leader, wanting only food and power, and led the ants to take over other countries and conquer the world. This made Meruem dangerous enough to be a target for assassination by the Hunters Association. After taking over the republic of East Gorteau, Meruem took an interest and board games, and would gather many champion players and challenge them to games. While playing a game called Gungi with Komugi, a blind girl that happened to be the regional champion, Meruem found that he couldn't defeat her so easily. Over time, Meruem gained genuine respect and affection for Komugi, even protecting her from animals that attack her. During the assassination attempt on Meruem, Komugi ends up being severely injured by an attack meant for Meruem. After ordering his guards to heal Komugi, Meruem battled against Isaac Netero, chairman of the Hunters Association. Following a brutal battle, Meruem ended up victorious, though Netero ended up detonating a miniature nuclear bomb in his chest in a final attempt to kill him. Though the explosion itself didn't kill Meruem, the poison from the blast was slowly destroying him from the inside, along with every Chimera Ant and Komugi. In the minutes before the poison killed him, Meruem managed to find Komugi, who was being hidden from him by one of his guards, and got to play one final game with her before the two died.
Immense Strength, Speed, & Durability: Due to being the king of the Chimera Ants, Meruem is much stronger, faster, and tougher than any human or ant. He can easily kill other Chimera Ants with a single strike of his tail, knock out people just by tapping their shoulders, reach supersonic speeds in seconds, and take Netero's strongest attack without a scratch.
Master Strategist: During his time playing Gungi with Komugi, Meruem managed to learn a lot about strategy and tactics. He has a supernatural foresight, letting him predict his enemy's moves with incredible accuracy. During his fight with Netero, Meruem was able to pick up on a pattern in his attacks so small that not even Netero noticed it.
Nen: Nen is the ability to use the life energy, or aura, of the user and manipulate it. Meruem's aura is so large, that it was assumed he could rival the firepower of an entire nation of Nen users, and his aura could spread out around an area larger than his palace fast enough to resemble a flash of light.
Ten: By forming a shroud of aura around the user's body, they can use it as a basic defense against Nen attacks, though it doesn't protect against physical attacks. Ten also slows down the user's aging process and keep their body from breaking down over time.
Zetsu: Keeps the user's aura from leaking out of their body, making them harder to sense and relieving fatigue, at the cost of leaving them defenseless against Nen attacks.
Ren: Expands the size and intensity of the user's aura to boost their strength and durability.
Gyo: Focuses aura into a single part of the body to increase its strength, at the cost of leaving the rest of the body more vulnerable. Using Gyo on the eyes allows the user to see someone else's aura, or other hidden objects.
In: An advanced form of Zetsu that hides the user's aura without forcing them to shut it off, making it perfect for sneak attacks.
En: Expands the user's aura in a spherical radius around them, letting them sense the shape and movement of anything that enters it.
Shu: Extends the user's aura onto an object that they're holding, enhancing its strength.
Ko: Concentrates all of the user's aura into one part of their body, making it incredibly powerful, at the cost of the rest of the body being completely defenseless.
Ken: A combination of Ten and Ren, using Ren to enhance the user's aura before enveloping themselves with it, providing greater defense than Ten.
Ryu: The real-time use of Gyo, shifting the concentration of aura between two body parts in quick succession.
Aura Synthesis: By devouring other living beings, Meruem can use their aura to boost his strength and aura size, heal himself, and gain their Nen abilities.
Metamorphosis: After eating Menthuthuyoupi, one of his royal guards, Meruem gained his ability to use Nen to shapeshift his body. Using this power, Meruem can grow extra limbs, extra eyes, and wings that let him fly at supersonic speeds.
Rage Blast: Another ability gained from Youpi, which lets Meruem condense his aura into a powerful energy blast.
Photon: After eating Shaiapouf, another royal guard, Meruem gained his ability to transmute his aura into photons and spread them throughout the surrounding area. Meruem can then measure the size, shape, quality, emotion, and other traits of whatever the photons interact with. By spreading the photons out in a sphere around him, Meruem can teleport to anywhere inside the sphere instantly.
Aura Shortage: If Meruem uses his Aura too much in succession, he will start to run low on it. If he uses all of it, he dies. However, Meruem's large supply of Aura prevents this from being a big problem.
Vulnerable to Strong Poisons: While the explosion from the nuke that Netero attacked Meruem with didn't kill him, the poison from the blast managed to finish him off. However, Meruem also happened to be the last Chimera Ant to die from the poison, despite being in the center of the explosion that spread it.