The SettingThe Nineties Anti-Hero is defined by the timeframe that spawned the trope. Just look at the trope title—this was born of The '90s, but also of what had come before it. Consider The '80s. This was a time when the Cold War was breaking down, and the Red Scare was slowly becoming a thing of the past, and the then-USSR was no longer the bogeyman that it had once been. They were something to be wary of for American audiences, but making them the villains did not automatically drum up Patriotic Fervor the way it once might have.
The Nineties was a time of massive political upheaval, and the inspirational heroes of the past—Superman, Captain America, even Batman—could be seen as too optimistic in a time where genocide, ideological war, and racial riots were widely publicized. Bad news travels quickly, and now the gruesome reality of what people were doing to each other could reach more people than ever before. Escapist fiction like comic books and movies adapts to its setting just like any other medium, and with this background, it's not too difficult to see why the Nineties Anti-Hero emerged.
The Nineties Anti-Hero is born of the things that creators and audiences learned from the unrest of the era—firstly, that infamy draws much more media attention than charity. Therefore, making characters in the classic Anti-Hero mold is a natural start. If a hero like Superman seems out of place in a world where genocide half the world away shows up on cable news, then maybe a protagonist who could survive in this new and uncompromising setting would attract an audience. As mentioned in the main article, Watchmen and Batman: The Dark Knight Returns set the stage for the setting by pulling away from the traditional view of heroes as The Cape, and that, combined with the broad reporting of the terrible things happening in the decades of the Eighties and Nineties, gave Nineties Anti-Heroes their dark, grim, violent roots.
The MethodsA fair number of Nineties Anti-Heroes are human, stated to use superior technology and training. In an era where the United States' conspicuous consumption was at its highest and the technological boom was moving in full swing, this choice seems only natural. These anti-heroes were ordinary human beings, albeit given their fighting abilities through suits of armor or powerful weapons, removing much of the messianic feel from the character. It reached out to those who would feel more insecure and less capable in an age where problems could visibly escalate quickly, and it gave readers a way to self-insert themselves into the setting of the comic books and Real Life at the time as potential problem-solvers themselves. The comics suggested that people who had enough training and enough firepower—things that were not impossible to have in real life, unlike superpowers—could do important, life-changing things and feel heroic.
Numerous examples of this trope are mutants of some description, following on from the popularity of Marvel's X-Men, and often tying back into them. Cable, for instance, was the son of Scott Summers (Cyclops) and Madelene Pryor, and Bishop worked for a police force that venerated Professor X. Most, however, seem human enough, even with their powers, and this ties in somewhat to the previous examples. By making the heroes seem human in spite of their powers and giving audiences an outlet for power fantasy, they could build characters that appealed to their core audience. Teenagers, being of an age where they could understand the things happening on the news and yet still feeling powerless as children, could project themselves into that same space, to feel special and powerful. As they were just reaching an age where they would experience large amounts of standardized testing, the desire to feel unique also played into the appeal of mutants who had powers yet remained their human appearance.
Finally, the prevalence of robots, androids, and high technology is based in large part on the growing technology boom of the era. The Eighties had already gotten many children of the era to see robots and cyborgs as the latest in 'cool.' The Transformers or Mighty Orbots might have kept the attention of young boys, but with the release of the Terminator films, the machine-that-looked-human set the new standard in visual effects, especially in scenes where some of the facade of humanity was ripped away to reveal the machine within. Since reader immersion in a machine's role can be difficult, however, the use of Powered Armor and the Hollywood Cyborg got around this restriction neatly. Now readers could imagine that they had armor or enhancements in some form or fashion, leading to much of the asymmetrical design of the era and the large numbers of cyborgs especially.
The use of rather fatal methods by Nineties Anti-Heroes takes notes from the same destructiveness of the era. Killing was seen as a reasonable solution to many of the more terrible problems, justified by the horrible acts perpetrated beforehand. Terrorism came into public consciousness in the era, and knowing that there was someone out there who would not hesitate to stoop to kidnap and kill wantonly led people to accept the notion of violence as the solution because the alternative was leaving the threat still there to harm the innocent. Similarly, the spike in news reports revolving around gun crime made firearms into a commonly understood occurrence, with the subliminal tie of weapons as power leading to the notion that these Nineties Anti-Heroes who didn't have super powers could still be powerful in their armament.
The Tie-InsNineties Anti-Heroes sold comics, toys, and video games, all highly popular and highly visible things to the target audience of the time—teenage boys. After the recovery from The Great Video Game Crash of 1983, games had gained just enough resolution, first in 8-bit, then 16-bit, to develop a fascination with and glorification of combat and fighting. Heavily armed heroes at the control of the player could blow away enemies, fight through fortresses to reach threatening bosses and take them down even if they were many times their size. In a way, Contra could be seen both as the classic run-and-gun platformer and the prototypical Nineties Anti-Hero game model. Since video game players at the time—again, mainly young to teenaged boys—had control of these heroes and could project themselves onto it, it's possible that creators were canny enough to see that giving their shared audience the same chance to self-insert themselves into the role of the character would reap the same rewards.
The Nineties and the Super Nintendo/Sega Genesis console wars led to a lot of appeal in the target area with the hardcore violence that they shared with many Nineties Anti-Hero type characters. See also the reference to Mortal Kombat in the quotes section, which set the stage for modern fighting games and the idea that more than simply defeating an opponent, killing them outright was a solution and a rewarding one at that (with points, later with potential changes to gameplay). These Anti-Heroes who used similar methods would go on to espouse similar messages in their actions, and the shared audiences of both were not incapable of seeing the parallels, and then buying the very games that followed in the step of Nineties Anti-Heroism and starring characters from the same. Both character creators and game developers benefited from readers buying games and gamers buying comics.
Ultimately, to sell their product, creators reached for not only what was perceived as 'cool' and 'mature' for its shock value, but also because of what that kind of character that would speak to their audiences of the era. In an age where the average teen could feel decidedly unempowered in a world which would not give them much to work with, the degree of power-fantasy escapism present in the Nineties Anti-Hero character type is what gave it its popularity at the time, but also what makes it look so cringingly uncomfortable and awkward now, as times and tastes change and the trope is viewed with nearly 20 years of hindsight.