Ben Reilly was the first successful clone of Spider-Man created by the Jackal. The Jackal, in his deranged grief over Gwen Stacy's death, pitted Ben against the real Spider-Man in Shea Stadium, putting both in identical costumes and allowing both to believe they were the true Peter Parker. After a heated fight, the two Spider-Men teamed up to try to save a clone of Gwen from the Jackal. In doing so, Ben seemingly died. Spider-Man dropped Ben's body into a smokestack, unable to think of any other way to deal with a dead body identical to Peter Parker.
However, the clone was not dead and literally rose from the ashes. Believing he was the real deal, he went home only to find Peter already there. The world as he understood it fell apart, and he left New York. In time, he adopted the name of Ben Reilly, a combination of Uncle Ben's name and Aunt May's maiden name
At the time of Ben Reilly's debut, Spider-Man had become a darker character who was losing touch with his life as Peter Parker. Ben was quite the opposite, having spent years away from the costume. In this way, he was more Peter Parker than Spider-Man was at the time. He was a purer version of Peter Parker that had not been burdened by the events that had recently dragged Spider-Man into brooding darkness, but his time away from costumed super-heroics had also left him rusty and less experienced.
It was the plan at this time for Ben to soon be revealed as the true Peter Parker rather than the clone and take over the Spider-Man identity for a time with Peter eventually being restored to it after seeing how Ben fared with readers. Originally, this entire three-act story for Ben was intended to run its course by the 400th issue of Amazing Spider-Man. Circumstances beyond editorial control saw to it that Ben's overall story would go far beyond that.
Both the over-dramatic name and the homemade costume of this identity were meant to be somewhat ridiculous, and it was unexpected how successful Ben as the Scarlet Spider became. As the Scarlet Spider, Ben gave readers a lighter and more familiar Spider-Man while Peter was still in his dark and brooding phase.
During this period, it was the plan that Ben really was the original Peter Parker and would eventually take the Spider-Man identity indefinitely.
Scarlet Spider, along with the Clone Saga in general, became so popular that Ben's time using this identity was extended significantly longer than he was ever intended to use it. The popularity of this identity got to the point where, even when it was time for Ben to become Spider-Man after many delays, his debut as Spider-Man was delayed even further to produce a couple of months worth of issues of renamed titles such as Amazing Scarlet Spider, Spectacular Scarlet Spider, and Web of Scarlet Spider.
After being delayed a great deal longer than originally intended, Ben finally became Spider-Man with a redesigned costume. Ben dyed his hair blond to distinguish himself from Peter Parker, despite supposedly being the true Peter, and settled into a civilian life working at a coffee shop.
Behind the scenes, the decision was made almost immediately by Bob Budiansky, with pressure from Dan Jurgens, to backtrack on Ben being the real thing and to restore Peter as Spider-Man. However, there was no clear plan for how to accomplish this, and completely flip-flop on the big move of making Ben Spider-Man.
