Marvel's Illuminati (consisting of Reed Richards, Tony Stark, Doctor Strange, Professor Xavier, Black Bolt, and Namor) had their hands in a number of events behind the scenes of the Marvel Universe. Among the events the group orchestrated was sending the Hulk off-planet, a maneuver that would become the inciting incident for Planet Hulk. The problem was, the Illuminati needed a good reason to effectively exile him.
Until then, Hulk rampages hadn’t actually left many people dead. The Hulk would occasionally attack an unnamed killer, or a hunter who just shot a deer (seriously), but they were never revealed to be civilian casualties. But the Illuminati was convinced it was just a matter of time before their fellow hero would go wild, and so, in order to justify the Illuminati’s decision to exile him, the Hulk saw his kill-count go up drastically. The official prelude to Planet Hulk saw the Hulk murder an attempted rapist with a single hand, but in the pages of the New Avengers: Illuminati special, things got even worse.
A retcon to a then-recent Hulk vs. Thing fight in the pages of Fantastic Four revealed that the rampage ultimately left twenty six civilians dead, including two children. It was a massive change to the character, and a slightly forced one at that. It was all an attempt to just justify the Hulk being shipped off world, and Marvel gave it to the Illuminati with an off-page mass murder.
In The Name Of Science
To be honest, the most dangerous thing to do around the Hulk is to try and use him to bolster your own mad science. This is how three separate people met their demise over the course of decades. The first of them was Armand Jones, who attempted to test out his power-draining device on a sleeping Bruce Banner in an issue of Web of Spider-Man #69. For his troubles, the scientist got swatted by the Hulk, and eventually had an entire building dropped onto him.
Morgan Clegstead was recruited to bring down the Hulk in Incredible Hulk #150, and was eventually transformed into the monstrous Crawling Unknown. The Hulk finally figured out how to bring down by stabbing the thing with a steel girder, and then letting the metal get hit by lightning.
The thing about each of those deaths is that they can all be seen as more of an act of manslaughter than murder. The death of Brian Banner was an accident, the retcon of his largest mass murder happened off-page and is therefore suspect. Even his actual on-panel kills were directed at people who had become monsters, either figuratively or literally. All of that makes last week's very horrifying murder of Doctor Clive so much worse.
The mad scientist is caught in the Hulk’s reformation of his body, quickly swept up in the wave of organs and limbs. As the Hulk re-forms around him, the doctor begs for mercy, and the Hulk just straight-up does not care. It’s an incredibly dark moment, something Bruce Banner reflects on when he regains control of his body with the sunrise. Plenty of people of have died because of the Hulk, yes, but this one felt darker than many of the others, more murderous. It speaks to the tone of the current run on the character, and the series' embrace of the horror that lies at the core of the Hulk.
The Immortal Hulk #8 is currently on sale, digitally and in comic stores.