Origin
Mycroft, real name unknown, was approached by Roxxon to use his incredibly high IQ and ability to link his mind into computer systems to destroy Stark Industries and thus eliminate Roxxon’s main competition. Mycroft operates from a large chair which he can connect his mind to and thus enter databases.
Creation
Mycroft was created by Len Kaminski and Tom Morgan, first appearing in Iron Man #316. He was named after Mycroft Holmes (The older brother of Sherlock Holmes) whom he also shares several characteristics with (For example, Mycroft Holmes is described as often being employed by Governments to solve their problems, much like Mycroft).
Mycroft was likely meant to appear in more issues, as his arc was left incomplete, but a change of writer meant that he was pushed aside.