Otacon (オタコン, Otacon), whose real name is Hal Emmerich (ハル・エメリッヒ, Hal Emmerich), is a character from the Metal Gear series who makes his first appearance in Metal Gear Solid.
Hal Emmerich is a genius programmer and anime devotee from which he derives his nickname "Otacon." Emmerich's family life was fraught with connections to nuclear weaponry--his grandfather worked on the Manhattan Project, and his father Huey was born on the day of the Hiroshima bombing. Both Huey and Hal's mother Strangelove worked with Big Boss during his days establishing a mercenary group not beholden to any nation. Huey would later commit suicide by drowning himself in the family's pool upon discovering that Hal had been seduced by his stepmother. Huey accidentally dragged his stepdaughter Emma in with him, instilling her with a lifelong fear of water. Determined to dodge the "family curse" of nuclear weapons, Hal strove to become a scientist to develop robots like the ones in the anime he enjoyed. He received multiple degrees from MIT and Princeton at a young age and was recruited by the FBI, though later fired for hacking into their databases.
Eventually, Otacon was hired by weapons manufacturer ArmsTech and made the lead engineer of the Metal Gear REX project. Otacon was lead to believe that REX was a solely defensive measure, only learning that it was intended as a nuclear launch platform after being rescued by Solid Snake from a Cyborg Ninja during the Shadow Moses Incident. During FOXHOUND's uprising at the nuclear disposal facility where development on REX was taking place, Otacon became taken with FOXHOUND member Sniper Wolf, seeing her affection for the island's wolfdogs and her kindness towards him as indicative of her character. Feeling guilty about his involvement with Metal Gear, he assisted Snake in rendering REX inoperable, though he was heartbroken when Snake killed Wolf. If the player submits to Revolver Ocelot's torture in Metal Gear Solid, he is the one who will escape with the player at the end instead of Meryl.
In the wake of the Shadow Moses Incident, Otacon and Snake formed Philanthropy, a UN-recognized anti-Metal Gear organization. This was in response to the rising number of Metal Gear derivatives that were cropping up after Revolver Ocelot leaked REX's design specs. Discovering information that the U.S. Navy was developing such a weapon, Metal Gear RAY, Otacon sent Snake in to the USS Discovery, an oil tanker on the Hudson River, to take photographic evidence of RAY. Believing the tip had come from Emma, Otacon intended to also use the mission to uncover information about the Patriots, which he had learned of while investigating another Metal Gear derivative. The plan was derailed by Ocelot, who used Snake's presence to frame him for destroying the tanker and causing a catastrophic oil spill. Two years later, Otacon assisted Snake and Raiden in their infiltration of the Big Shell facility that, while ostensibly meant to contain the oil spill, was secretly the development base for Arsenal Gear, the Patriots' new Metal Gear-like weapon. During the Big Shell incident, Otacon was reunited with Emma, who was the developer of GW, Arsenal Gear's AI system. Otacon and Emma reunited, and she helped him and Snake upload a worm cluster that was supposed to have destroyed GW before Dead Cell member Vamp killed her.
After the Big Shell Incident, Otacon became the caretaker of Olga Gurlukovich's daughter Sunny. Discovering that Snake was aging rapidly, Otacon remained Snake's primary support throughout his final missions to assassinate Liquid Ocelot. During this time, he became romantically involved with Naomi Hunter, and was predictably distraught when she deactivated the nanomachines in her body that were keeping her cancer at bay. After Snake defeated Ocelot once and for all, Otacon remained by his side to serve as a witness to his final days.
Main article: Codec Conversations
Otacon appears in Shadow Moses Island and contacts Snake via Codec and informs about the fighters in the battlefield if a down taunt is inputted quickly, resulting in a Smash taunt. Otacon informs Snake about Donkey Kong, Diddy Kong, Link, Samus, Yoshi, Kirby, Captain Falcon, Mr. Game & Watch, Pit, Ganondorf, Sonic and R.O.B. If Snake gets KO'ed while Otacon is on the communication line, he says the infamous line: "Snake? Snake? Snaaaakkkkeee!"
Otacon, under his real name Hal Emmerich, appears as a spirit in Ultimate, represented by his look in Metal Gear Solid 4: Guns of the Patriots. In his Spirit Battle, he is represented by Dr. Mario. He also returns in Snake's Codec Conversations as they are reused from Brawl.