Mastiff

Mastiff was a type of Unmanned Gear deployed in 2018. It was hulking and had its hands hidden in armor, with Browning M2HB turrets on its wrists. They are also capable of pummeling an enemy into the ground, putting an enemy into a single arm stranglehold, and, if all else fails, doing a mid-air kick with both feet to knock the enemy back. Raiden, as a Maverick agent, managed to somehow find design specs relating to the Mastiff during or prior to the mission where he sustained severe injures. Maverick later retrieved his arm and located two blueprints of the Mastiff, the latter of which detailed its head and was stumbled upon while Maverick was recovering data relating to Raiden's time at Force XXI, although they required passwords to get to the encrypted files, and the blueprints themselves ended up corrupted, due to the damage to Raiden's arm. Desperado Enforcement LLC utilized Mastiffs during battle. Raiden, during a mission into Mexico to locate a research facility, ended up being ambushed by a Mastiff in the sewers, although he quickly destroyed it to prevent it from alerting Desperado. Several more Mastiffs were also nearby patrolling the sewers, which Raiden ambushed/evaded via the catwalks above.

Their overall behavior, including their running movements and beating their chests in an aggressive stance, are similar to gorillas, Just smarter becaue of their abilities to do chokeholds and dropkicks

Behind the scenes
The Mastiff first appeared in the Metal Gear Rising: Revengeance E3 trailer in 2010 (then known as Metal Gear Solid: Rising) as an enemy that Raiden ambushed and proceeded to cut up via zan-detsu, before absorbing its spinal cord energy and then crushing it (although it was not identified as such). It was based on designs made by Yoji Shinkawa that were originally intended for Metal Gear Solid 4: Guns of the Patriots, as a design for the Beauty and the Beast Unit.

The Mastiff was not given a name until after the "Make It Right: decryption" viral marketing site uploaded artwork of the Mastiff that required a command key code to access, with the in-universe explanation given on the Metal Gear Solid Facebook page being that Maverick located an encrypted file cluster that was password protected, and found clues to the password in the names "Anatolian", "Alpine", "Bully Kutta", "Cane Corso", "Bordeaux", "Pyrenean", and "Neapolitan", all of which are breeds of the mastiff dog breed.

According to a leaked achievement trophy list for Revengeance, destroying 10 Mastiffs in a playthrough will award the player with the achievement/trophy "Silverback" a reference to their gorilla-like nature.