The main question people have had about a Venom movie since it was announced is whether one of Spider-Man's deadliest foes can carry a movie by himself, especially as the hero. The film will see Tom Hardy step in the shoes of Venom's most famous human host, Eddie Brock, but over the past several years, Marvel set about making Venom a hero with the help of another Spidey antagonist turned good guy: Flash Thompson.
It all began with some slight adjustments to Flash's backstory. Like Tony Stark, a chunk of Flash's history used to revolve around the Vietnam War. He was drafted during the Stan Lee/John Romita Sr. era of The Amazing Spider-Man, well after he and Peter had begun to move past their high school days. Changed drastically by his time in the Army, Flash came home a war hero, but dove headfirst into alcoholism, like his abusive father before him.
Fast forward to 2007 and the ever-controversial "One More Day" storyline. following the magical dissolution of Peter Parker and Mary Jane Watson's marriage (and entire relationship), Flash's service was updated so that he'd served in the Iraq War, the character inspired by a combination of post-9/11 patriotism and Spider-Man's example. His platoon was ambushed and, though wounded, he saved his unit and commanding officer. Unfortunately, his legs were so damaged they had to be amputated below the knee. Having earned the Medal of Honor, a recovering Flash moved back to NYC.
Meanwhile, the Venom symbiote, having been bonded with Mac "Scorpion" Gargan as part of Norman Osborn's Dark Avengers, was forcibly separated from his then-current host when that team was taken into custody. Held by the U.S. Government, the symbiote was the center of a new incarnation of Project: Rebirth (named after the super-soldier program that created Captain America), with scientists learning a person could be bonded to it for 48 hours before it'd take control.
Needing a test subject, the military approached Flash and, wanting to continue serving his country, he agreed. Surviving the process and armed with tranquilizers to stabilize his control over it, Flash and the symbiote allied as "Agent Venom," working covert operations on behalf of US interests. This led into a new volume of Venom, initially written by Rick Remender and pencilled by Tony Moore, Lan Medina and Tom Fowler, among many others, where Agent Venom never had it easy.