Otacon is snakes partner, well he isn't officially his partner until Metal Gear solid 2: Sons of liberty. His real name is Hal Emmerich, and he was assigned by President Baker or Armstech to develope a "anti-nuclear" TMD. During the process, the terrorists who were former members of Fox-hound took control over the Shadow Moses Compund.Hal was allowed to stay, in order to finish up preperation to Rex. Snake encounters him in his lab, after a nasty run in with Gray Fox. Otacon from there is told his anti nuclear tank, will instead be used to launch missles to anywhere in the world, and joins Solid snake, via Codec and stealth camoflauge to give you useful help through out the game.

In MGS2, Hal has a little sister E.E. AKA Emma Emmerich. (Her profyle will be posted shortly)

Otacon's past is a bad one, Apparently his real mother either died or left, leaving his father to marry his step mother Julie. Julie already had a young daughter, whom became Hal's step sister. But Hal's life was turned upside down when his father found out about his affair with his step mother. While they swam, their father killed himself in the family pool, Hal was so distrought he left and vowed to never bother his family with his 'useless-ness' again.