In the original story, Porter created the drug from scratch in a contest of intellects and egos with other scientists, making use of some rogue military funding and the high crime and corruption of the Gotham City area as a means of testing, covert supply and distribution. Porter found the still-young and relatively new figure of Batman intriguing, determining that someone who could pull off the physical feats he did was stable enough to be a true test subject. In order to outwit a man already credited with a formidable intellect, Porter developed another drug, this one an intelligence enhancer that had the added "benefit" to his view of deadening his emotional attachments. If this drug was a mental variant of Venom, it was not stated as such, and has not been seen or referred to since.
In his brain-enhanced and emotionally dead state, he concocted a scheme by which he would stage the kidnapping and murder of his own young daughter, with Batman arriving too late to save her. Guilt-ridden and apologetic, the younger more naive Dark Knight accepted Porter's offer of Venom, for a time enjoying the easier time it gave him in his crusade. He at first brushed off the signs of addiction, as well as his increasing tendencies towards raw brutality while under the drug's influence. When Porter, whose operations were being scrutinized by the GCPD, ordered Batman to kill James Gordon, Batman realized the predicament he'd placed himself in when he almost went through with the order. With Alfred's aid, Batman locked and isolated himself in the Bat-Cave for a month until the drug cleared from his system entirely. Confronting Porter and his sponsor, the outlaw General backing the program, he was forced to fight the General's Venom-enhanced son, whom the General had despised for being, in his view, 'soft'. As Gordon and his men arrested Porter and shut down the operation, Batman made sure to confiscate Porter's intelligence-enhancing drug, perhaps realizing that Porter might still have Venom hidden on him, did not confiscate that. Porter reportedly was killed during a frenzied break-out attempt, his strength enhanced but his mind diminished by withdrawal symptoms, a pattern of reliance on his 'smart-pills' now making normal thought harder for him to deal with, and the mental reduction caused by Venom's side-effects. Some remnants of the drug still circulated for years thereafter, haunting Batman among others on countless occasions.
In later stories, Venom was given a history and a legacy. It was revealed that technically, the real creator of the drug was Rex Tyler, the Golden Age Mystery Man and member of the Justice Society Of America called The Hourman. Called Miraclo in those days, its addictive properties were slower to develop, and its strength-enhancement, as evidenced by the hero's name, only lasted 60 minutes. Porter was responsible, however, for refining and enhancing it on several levels, very few of them positive. Just as Porter had done this with Miraclo to Venom, so did someone else do this to Venom in the video-game based Batman Arkhamverse. Doctor Penelope Young of Arkham Asylum sought to create a Venom derivative called Titan, ostensibly to treat the otherwise irredeemably insane. One such irredeemable, the Joker of that continuity, seized control of the project, shaping the entire history of that gaming universe. Indeed, all four games in that series are haunted by what Porter began.
Already cold and psychotic, Porter managed to hit the younger Batman in a vulnerable spot he hadn't realized he had, drew him in far enough to almost cross the line forever, and left a legacy in which Bane was not even the worst result.