The Rank is a label given by the Maverick Hunters that indicates how powerful and efficient a Reploid is. When the subject is a (potential or active) Maverick, the Rank measures their level of threat. The ranking had its criteria changed many times over the decades due to the technological advances and improvements in the methodology. Still, it may seen as an imprecise label since X was classified as a B-Rank Maverick Hunter for a long time even after defeating several "superior" Reploids like Sigma many times, only because of his aversion to violent methods and frequent hesitation. The ranking is also used by bounty hunters as a reference of difficulty and consequently higher bounties.
Around 2193, the ranking follows this order (intermediary Ranks like AA have been omitted since they are for specific cases):
Rank E - Civilian Reploids and small, harmless Mechaniloids are considered to be in this level of threat, as they can be suppresed easily.
Rank D - Rookie Hunters usually begin in this level. Most bandits and medium-sized berserk Mechaniloids belong to this level of threat and can be defeated by the local police.
Rank C - The level of power expected from most mass produced combat Reploids. The battallions of the Maverick Hunters are mostly composed of C-Rank Reploids, although their training process is expected to raise their Rank to B. This is also the threat level in which Maverick Hunters start to be required in emergency. Members of the Neo Maverick Army in this level are labelled as Pawns.
Rank B - Maverick Hunters in this Rank have attributes considered to be satisfactory or more. This is the minimum rank required to make part of the 17th Elite Unit. A Maverick who survived a battle against B-Rank Hunters is automatically set to B level or higher. The analogue NMA ranks are the Warmonger and Warchief.
Rank A - Maverick Hunters beyond this Rank are very experienced and usually lead Units. Mavericks with this label tend to be regional threats, as most of the A-Rank Mavericks lead crime networks, black markets or simply have the power to influence many other Reploids. The latter can evolve to S-Rank when they put in action some kind of dangerous and destructive operation, such as Saturn, Kran and Kerbekeros. There are rare cases of A-Rank Mechaniloids that are extremely resistant and bear a high destructive power, like Gigantex.
Rank S (Special) - The highest possible ranking. To be labelled as a S-Rank Reploid, one must show outstanding combat skills, extreme intelligence or abilities that make them unique and unmatchable in their field of expertise. X and Zero are the only Hunters alive who managed to achieve this rank. Mavericks with this rank are a threat to the whole world, such as Sigma and Dynamo.