Meruem had a rather humanoid build for an Ant. He was muscular and toned, despite his relatively small frame as compared to his servants. He had two long antennae on his ears and a large shell-like armor over his head that resembled a helmet. There were dark pigmented areas on his arms, legs, chest, and head. Meruem was always barefoot. He possessed a powerful tail equipped with a stinger that served as his weapon. Both his hands and feet had only four digits each.
For some reason, he looks nothing like an Ant, and his look is somewhat reminiscent of an anthropomorphic snake or Cell from Dragon Ball Z. Meruem was initially a cruel and violent leader. The Queen's intention to give birth to a perfect offspring was reflected in Meruem's haughty mentality. He considered himself superior to all other forms of life and felt no concern for his dying mother after his birth. Meruem was merciless, killing and cannibalizing any Chimera Ant he deemed to be disrespectful, although he still held respect towards the strong, complimenting Neferpitou for emerging relatively unscathed from an attack that had killed many. He hated saying the same thing twice, and he would often tell others that he would not repeat himself. He showed no empathy towards humans and viewed them as nothing other than a food source, killing and devouring a child not long after his birth and subsequent departure from the Chimera Ants' nest, only to spit out the child's flesh and calling it disgusting compared to the sensations he occasionally experienced while in his mother's womb.