"Tit for tat, Mr. Hero. Tit for tat."-Karl Hertz to Smith
Karl Hertz is the main antagonist in the 2007 film Shoot 'Em Up.
Karl Hertz sends his men to go after a pregnant woman. Smith goes after them and kills one of the hitmen with a carrot. He then shoots some of the other hitmen and helps the woman deliver the baby. One of the men shoots the woman dead, so Smith takes the baby with him and then on the roof, he shoots at a sign, when Hertz is on the roof, he shoots at the "L" light on the sign. He shoots one of his men for failing him. While Smith stops at a park and puts the baby on a merry-go round. As a woman approaches the baby, Hertz shoots the woman in the back with a sniper rifle. He tries to kill the baby, until Smith gets him off the merry-go round after making it spin. He unloads his gun, making him unable to get a clean shot. He heads to a brothel and asks Donna where Smith is, and she tells him she doesn't know what he's talking about. Smith then shows up and forces Hertz into the hall.
Hertz finds out that he's out of bullets since he fired all his shots at the wall. He takes out a knife, then Smith shoots him in the chest. Later on, Hertz wakes up, wearing a bulletproof vest. He gets a call from his wife, and he tells her he'll be away for a litle while, and promises he'll be at home to celebrate his son's birthday. He then calls his employers that he needs more people for the job. He sees the pawn shop, where Smith and Donna got a bulletproof vest. After he asks his men to choose which card for his son, he orders the henchmen to kill Smith. The hitmen are killed by Smith. Hertz then asks if Smith was really that good. Hertz is then seen at a gun factory, where he talks to his boss, Hammerson. He finds out who Smith is.
Smith finds out that Hammerson and Hertz are trying to kill the baby because Senator Rutledge needs the baby's bone marrow to live. He chases Smith on the bridge and tells his driver to run the baby over, but then he finds out that it was a robot baby. Hertz and Hammerson arrive on the plane and reveal they made a deal with Rutledge. Smith takes Rutledge hostage in the hatch and shoots him dead. Hertz, Hammerson and some of their remaining men take Smith hostage and Hertz demands to know where Donna and Oliver are. Smith tells him since he killed Rutledge, Hertz still can't hunt them down.
Hertz tells him they'll cover it up and saying the plane went down and Rutledge went missing. Hertz breaks some of Smith's fingers. Hertz grabs a scalpel, preparing to stab Smith with it, but Smith head butts him. Smith blinds Hammerson with the blood, forcing Hammerson to kill himself. Smith puts his hand in the fireplace, causing the bullets to hit Hertz in the chest. The severely wounded two men get up and raise their guns for their last dual. Smith is faster on the draw, he then shoots Hertz again, blasting a hole through his body, finishing him once and for all.