It is a superhero setting! Unlike a lot of superhero settings, it is basically a decent, functional place to live in which the whole 'superhero/supervillain dynamic' is acknowledged to be a short-term cultural phenomenon that will probably stop existing at some vague point in the future, and the majority of superpowered people just make large salaries using their powers for ordinary things. There is an in-universe history running roughly from 1920 to 2017, and advancing as I write more stuff.
All powers in the setting are ultimately genetic; if you have a specific rare hereditary condition, you will, absent modern medicine, die as a child. If you survive, than, once in your life, if you are put under sufficiently extreme mental/physical stress, you will gain superpowers! What powers depend on what kind of stress, circumstantial details, your instincts, and a whole lot of random chance.
If the stress is a simple physical threat, you get required powers not to die from it! If these powers would themselves cause you to die, or if you are under threat from multiple things (e.g. heat, falling ceiling and smoke inhalation) there's a brief window where you can continue manifesting more powers to cope with the situation. Powers gained from surviving danger are termed Survivor powers; the boring end is "you are immune to pneumonia" and the extreme end includes mind control, constructing a force-field shell around you strong enough to stop a train, or controlling any water in most of a mile's range.
If the stress is mental stress from an outside source, you get the ability to deal with this mental stress by changing how the outside source functions. The most common outside source is 'the laws of physics won't let me build a COOL THING I KNOW IS POSSIBLE' and you get reality-warping mad science ("Tinker" powerset), ranging in strength from 'technically this isn't possible with my materials' to 'AHAHAHA REALITY IS MY PLAYTHING'. Other examples of Warper powers include weather control (the weather is not RESPECTING MY SUFFERING) and teleportation (I am in the wrong place and I NEED TO BE ELSEWHERE).
If the mental stress is from depression - you really just hate yourself and hate your life - you become the someone else you would most rather be. There are at least four pseudodraculas, an alien invasion lead by a Galactic Conqueror, three faeries, one explicit D&D character, and the Messiah of Mozambique. There are also people who just finally, finally got the chance to be pretty.
The overwhelming majority of supers with genetic powers are Survivors; Idealists are a small minority, Warpers are somewhere in between. There are also a lot of people who were given powers by other supers, usually tinkers; granted powers do *not* come with required secondary powers, and are therefore either very weak or highly user-unfriendly. Most power-granting tinkers capable of it are making stupendous amounts of money making very rich people immortal, in a way similar to how most large-scale-construction tinkers are making perpetual motion machines for clean energy and the majority of super-strong survivors are lifting heavy objects (or the equivalent) for a living. Around 10% of the superpowered population maybe vaguely plays the 'cape game', very very vaguely 2-1 heroes to villains.
Powers are semi-formally ranked from A to D (the scale originally just meaning 'so, how much do you need to panic when you hear an X-ranked supervillain shows up in town?) but these are wide, wide categories and power is heavily non-transitive; there are mediocre supervillains who everyone acknowledges could easily beat or evade one of the world's strongest heroes in a fair fight (because his only power is punching and he can do nothing against people who can go intangible, say), and A-ranked superheroes with purely offensive powers and no defenses whatsoever who could theoretically be killed by any guy with a gun, so a lot of fights (and a lot of supervillains picking what city they want to try to commit crimes in) involve both sides trying to pit their superpower against the other side's mere-ordinary-human lack of superpower.
Superheroes have a semi-complicated legal role with state-granted insurance to pay for damage done in exchange for emergency services work, as well as small salaries, but don't need to do all nearly as much paperwork or follow as many orders as police officers do, and can set their own hours. Supervillains are wholly aware that a dramatic, booming mastermind (or a romantic and dashing rogue, or a megalomaniacal mad scientist) will not only make the news faster than a common criminal who merely happens to have a few tricks, but will probably get a lighter sentence and also fan mail. The expected incentives occur, at least in the US, Canada, Mexico and Japan - there are a lot fewer supervillains outside the area American culture has colonized so thoroughly, and a great many of them move to America, where people will react properly to a supervillain instead of being acutely embarrassed that a grown man is actually dressing up like that.
The setting's generally acknowledged Leading Superhero Team is the Atlantic Six, which that has had varying membership (the only hero on all incarnations is the Survivor, who is immortal, indestructible, and the world's physically strongest man) but the next-to-most central member is Minerva, who went from being 'one of the world's strongest tinkers' to being 'the army of hive-minded superpowered robot duplicates of herself she created in advance' after she died, without at any point losing team membership. Most people who talk about the World's Greatest Superhero mean one of them, at least in the English-speaking world, though there's a lot of debate about whether the concept is even meaningful.
The World's Greatest Supervillain, professionally speaking, is/was the Titanium Tyrant (1947-2013), a charismatic Armored Megalomaniac (and the inventor of non-tinker powered armor) who lead his own supervillain team and inspired more imitators than any of his rivals. He eventually took over his own Caribbean island, which is a haven for world supervillains from 1993 to 2013, when plot happens.
The World's Greatest Supervillain, death toll speaking, is Voidwrath, who is a teenage boy's idea of what a super cool badass villain would be. He rules a space empire (which cannot be located with any telescopes) and regularly invades Earth and comes up with a new power and a new lieutenant every time he's beaten. Nobody has figured out how to kill him hard enough that he stays dead.