Otacon, real name Hal Emmerich, is a character from the Metal Gear series who makes his first appearance in Metal Gear Solid. He is the one who helped design Metal Gear REX, unaware of its true purpose. With guilt all over his feelings, he assists Snake in dissembling Metal Gear REX. However, he is slowed down by a love of the famous sniper, "Sniper Wolf." If the player submit to torture in MGS, he is the one you will escape with.
He returns in Metal Gear Solid 2: Sons of Liberty as part of the Philanthropy group, an anti-Metal Gear organization. He guides Snake through the tanker, Discovery and the disguised oil-cleanup facility, the "Big Shell". During the Big Shell chapter, Otacon's half-sister, Emma Emmerich, holds the data chip to implant a computer virus to stop Arsenal Gear's computer AI, GW. She is stabbed on her way to the computer room and later dies. Otacon's father had committed suicide prior to Metal Gear Solid and Otacon's stepmother had a seductive relationship with him (which is the cause for Otacon's father's death and some of Otacon's own psychological problems).
His nickname is derived from "Otakon", as his main interests are anime and manga. His main motive for going into weapon design was to build real-life Fighting-Robots, his fantasy from a young age. (Zone of the Enders is cited in the Gamecube version and Policenauts in the Playstation version, being that MGS, ZOE and Policenauts are all made by Kojima himself.) Overall, the development of Otacon is from a cowardly weak man, to a man who stands for courage.
Otacon appears in Shadow Moses Island and communicates Snake via Codec and informs about the fighters in the battlefield. Otacon informs Snake about Donkey Kong, Diddy Kong, Link, Samus, Yoshi, Kirby, Captain Falcon, Mr. Game & Watch, Pit, Ganondorf, Sonic and R.O.B. And, if Snake happens to get K.O.ed while Otacon is on the communication line, he says the infamous line no Metal Gear Solid player wants to hear- "Snake? Snake? Snaaaakkkkeee!"