Everyone—hero and villain alike—has some kind of alter ego. Ghost is no different, but since being introduced in 1987 via Iron Man #219, readers have never been given Ghost's real identity. His story has been known, but never who he actually is.
A whiz at computers and tech with genius-level intellect, the person who would become Ghost is essentially a guy consumed by a job in the world of IT. Employed by a company named Omnisapient, he was known for creating "Ghost Tech," which was a computer processor with the ability to physically change and adapt to its environment, effectively preventing the processor from overheating. He became extremely successful and known for his revolutionary work in the field, until he fell in love with a co-worker and dropped everything to be with her. Their romance was cut short when she was killed in an explosion at her apartment. Already devastated by her death, he was hit with an even harder blow when it was discovered that she wasn't really in love with him, but paid by Omnisapient to help keep him at their beck and call; the company ended up killing her when she tried to blackmail them for more money.
This revelation pushed the engineer to the edge and he started wiring his own skin to the Ghost Tech processors. When Omnisapient found out that he knew what they did, they hired a hitman, who blew up the his building. The explosion didn't kill him but did fuse the processors to his flesh, turning him intangible and gave birth to Ghost. Hellbent on taking down corrupt corporations (on some Mr. Robot sh*t), he murdered the Omnisaient board of directors, as well as the hitman they hired.
Ghost then erased all traces of his past life, literally becoming a ghost. His hatred for corporate entities have turned him into a skilled hacker, and has had him butt heads with Marvel heroes like Iron Man, who's alter ego Tony Stark ran Stark Industries, a company with its hands all over the Marvel Universe.