Relative to its size, the chewing muscle of the jaw often called the strongest muscle in the human body is the masseter. Located at the side of the face, it runs from the cheekbone region to the lower jaw and helps elevate the mandible when the mouth closes.
The masseter is one of the four principal muscles of mastication, alongside the temporalis and the medial and lateral pterygoids. Its superficial and deep portions work together to generate powerful biting force. The mandibular division of the trigeminal nerve supplies it, allowing the brain to control chewing movements.
The “strongest muscle” label needs context. Strength can mean maximum force, force relative to muscle size, pressure, endurance or mechanical advantage, and different muscles may lead under different definitions. The masseter is a defensible popular answer when the comparison is explicitly relative to size or biting force.
The gluteus maximus is the largest muscle in the human body and is vital for hip extension, but it is not the usual answer to this jaw-muscle question. The temporalis also closes the jaw, yet the masseter is the prominent muscle most associated with powerful biting.