In both the comics and on film, Venom is known for his rivalry with Spider-Man, Carnage and other symbiote characters. One of the more unknown symbiotes actually just debuted in Venom: Let There Be Carnage, or at least his human host did. Detective Patrick Mulligan was a prominent part of Venom 2, but he hasn't been part of the comics for a while thanks to the son of the devil.
Mulligan's career as Toxin was rather brief, with the attempted hero being more of a side character to Venom, Carnage and Spider-Man than a real solo character in his own right. His death was also somewhat overlooked, with Toxin later taking two more hosts and everyone essentially forgetting Mulligan ever existed. With the character debuting on the big screen, however, there's a chance that this could be undone. Here's a look at the comic book death and birth of Patrick Mulligan's Toxin.
The Birth of Toxin
Patrick Mulligan debuted in Venom/Carnage #1 by Peter Milligan and Clayton Crain, with the Toxin symbiote bonding with him in the next issue. The still unruly symbiote was birthed by Carnage, who had no interest in spawning a potentially stronger creature. When the deed is done, Carnage is left weakened and unable to kill his "child." Thus, Toxin bonds to the nearby Detective Patrick Mulligan, with Mulligan's own morals and Toxin's strength suggesting that he'll become a hero instead of a villain like Carnage. Venom and Carnage attempt to defeat Toxin, but he proves to be too powerful.
Though Mulligan tried to be a good guy, he found himself fighting the Toxin symbiote's dark desires as much as he did evildoers. Despite this, he was trusted enough by the heroic Spider-Man to help him round up escaping supervillains. This was made more complicated by his having left his wife and child due to fear over the symbiote, but in time, he proved himself a hero and kept Toxin in control. Sadly, this heroic career wouldn't last long for Detective Mulligan.
The Death of Detective Mulligan
In Venom #12-13, the Toxin symbiote is removed from Patrick Mulligan through murderous means. Blackheart, the son of the demonic Mephisto, kills Patrick Mulligan and places his symbiote in an underground lab beneath his Devil's Den front operation casino in Las Vegas. Upon discovering that a symbiote was up for grabs, Spider-Man villain Jack O'Lantern made a bid to retrieve it, blackmailing Flash Thompson, a.k.a. Agent Venom into retrieving it for him.
The Venom symbiote takes over Flash at one point, intent on killing Toxin out of fear of the threat that he could cause. This is circumvented when Jack O'Lantern shows up to stop him, but they also learn what exactly Blackheart was doing with it. He used the original sample of the symbiote as part of a satanic ritual to unleash hell on Earth, and that wasn't all that he did with Toxin. He also bonded a section of Toxin to clones of the mutant X-23, creating his Symbiote Warriors which acted as bodyguards for him.
Agent Venom, along with Jack O'Lantern, Ghost Rider and the real X-23 eventually defeated them, with Toxin resurfacing afterward. After trying to rid the world of symbiotes, Eddie Brock was instead forcibly bonded to Toxin. This fusion would last into the All-New, All-Different Era, with Brock eventually giving up Toxin and later becoming Venom again. Since the events of King in Black and the recent Extreme Carnage, Toxin has taken the new host of Bren Waters, the son of the current Guardsman. Sadly, Patrick Mulligan has long since been forgotten in the comics, with even his death being overlooked when it occurred. Given how mysterious this death was, however, not to mention the character's theatrical debut, the original host for Toxin could one day return to the comics.