The Birth: This is the tricky part. If Ben Reilly is the clone of Peter Parker, then he was created by Miles Warren, a brilliant scientist and professor at ESU. Miles had haboured a crush on Peter Perker's late girl friend; Gwen Stacy. When Gwen was killed by the Green Goblin, Miles Warren blamed Spider-Man for her death and went off the deep end. When his attempt to kill Spidey by sending the Punisher after him didn't work, he tried to clone Peter Parker and Gwen Stacy. (Why he chose Peter in his fantasy is something I'll never know) He had already adopted the identity of the Jackal. The clones degenerated and died. But finally the Jackal succeeded in cloning Spider-Man.
Somehow he was able to render Spider-Man unconscious as well as his clone. When the two awoke, they both believed they each of them was the real Spider-Man and they battled each other. A Spider-Man is a Spider-Man - when they found out that Miles had kidnapped Ned Leeds and had wired him to a bomb, they rushed in to save Ned. In the end, Warren himself; persuaded by a Gwen clone, saved Ned just before the bomb exploded, killing the mad proffessor. Also presumed dead in the exploion was one of the Spider men.
The only standing arachnid left the clone's body in an industrial smokestack and went home, convinced he was the real Peter Parker.
That's when the life of Ben Reilly starts. The clone was not really dead. He awoke and went home. But seeing Peter with Mary Jane, he ran away to lead a new life. He took the name of Ben Reilly, met Seward Trainer and basically hung around with him for quite a while.
One day, Ben Reilly learned that Peter's aunt; May Perker had a stroke and lay comatose in hospial. That's when Ben Reilly crawled out of the woodwork. Pretending to dial the wrong number, he kept in touch with May Parker.
When Ben Reilly learned that Judas Traveller was fighting Spider-Man, he donned a crude costume to disguise his identity and helped Spidey in the battle. Parting ways with Spidey, he kept the super hero bit and fought other villains such as Venom. Not knowing who this new kid on the block was, the Daily Bugle reporter, Ken Ellis dubbed him "Scarlet Spider"; a name that eventually stuck to him.
..... The Scarlet Spider made his debut in Amazing Spider-Man #149 and his graceful exit from this world took place in Peter Parker: Spider-Man #75

The Alter Ego: Ben Reilly has exactly the same qualities of Peter Parker, after all he is his clone. In the short span of his life he was not able to get into a staedy relationship with the fairer sex. Initially he worked as a waiter at Club Noir and later on at the Daily Grind, a coffee shop.

The Legend: Scarlet Spider used pretty much the same equipment that Spidey uses. Web-Shooters, Spider-Tracers along with his own "impact webbing" and Stingers made him an arachnid to be rekoned with. Some time later Peter and Ben were again reunited as they both received a telepathic "call" to a secret lab in the Catskill Mountains. There a clone of the late Miles Warren a.k.a the Jackal awoke and suggested that in fact it was Ben Reilly who was the real deal while Peter Parker was the clone. In the battle tha followed, the spider duo got rid of Jackal's clone but later a third clone of Peter Parker emegred from the cloning pod who soon became convinced that it was he who was the real Parker. He later joined Kaine; a clone who was the first experiment of the Jackal. Kaine dubbed this new version of Parker as Spidercide.
Soon after this, Aunt May Parker came out of her coma but died shortly after that. And to add to Peter's misery, he got arrested for the murder of a cop on basis of his fingerprints being found on the muder weapon. Judas Traveller got Peter busted out of prison. Peter then went away "truth searching" while Ben posed as Peter Parker. It was during this time that the failed clone of the Jackal - Kaine - revealed himself to Peter and confessed the truth.
Soon after this, Ben, Peter and Mary Jane went to Seward Trainer's lab where he determined that Peter Parker was indeed the clone of Ben Reilly. That meant that Ben Reilly was really Peter Parker.
A new chain of events opened up. The Jackal returned and convinced Peter to join him and Spidercide. Ben Reilly found Peter and rescused him from the dozens of other clones and drummed some sense into the former web slinger.
The talk made Peter focus on his wife; MJ and the baby that was coming. Ben Reilly, meanwhile swung about as the Scarlet Spider. It was while fighting the new Doctor Octopus that Peter realized he had a responsibility to his family and thus decided to give up the role of Spider-Man.
Scarlet Spider had also become a member with the New Warriors. The Scarlet Spider fought Doc Ock and defeated her, but not before she realised a fake Scarlet Spider in the city to do damage. In order to clear his name, Ben Reilly donned the one mask that he knew Doc Ock could not tarnish - Spider-Man.
After this, he remained in the Spider-Man tights, although he changed the costume a bit. He had skirmishes with the reformed Sandman, fought Carnage as well as Kaine.
..... Later on Peter Parker and Ben Reilly found out some interesting revelations while snooping around. It seems that the mysterious Judas Traveller was a mutant with the ability to control people's perceptions of reality. Seward Trainer had been hired by another mystery man called Gaunt for some unknown deeds. Guant worked hand in hand with a group of people called the Scriers who were financed and controlled by Gaunt's employer. The biggest surprise turned out to be the mastermind of the entire plot - none other than the original Green Goblin - Norman Osborn! Norman found out about Miles Warren's cloning experiments. Once Ben Reilly was created, Gobby hired Seward Trainer and Mendel Stromm a.k.a Gaunt to tear Peter Parker's life apart.
When his hoax was out, Norman Osborn tried to kill Peter Parker. In an effort to save Peter, Ben jumped in front of the goblin glider, impaling himself.
Nuff said, that was the end of the Scarlet Spider. At least, in an effort to keep a good hero alive, Marvel has not dumped another clone on us. But with the number of Peter Parker clones that were running about, there's no telling when one can crawl out of the ashes and become the Scarlet Spider.