Heroes that can actually serve very important purposes and need to be kept alive, or simply kept around at all costs. In other words, these heroes cannot be destroyed/killed or something terrible might happen. These characters are similar to Necessary Evil characters, but are obviously opposed to their alignment. These characters are usually created to keep the story relatively three dimensional. Examples include:

1. Heroic Organizations/Teams keeping the international evil threats at bay (Autobots protect Earth from the Decepticons, the evil robotic team bent on tyranny, Justice League is known to protect the world from inter-dimensional threats, and the Power Rangers has the purpose that involves standing up together against the interdimensional threats of the world. It also includes those that protect the inhabitants from any malicious threats and attempt to help and be friendly with civilians whenever they can)
2. Employees and employers that actually are capable of doing their jobs and it's made very clear the business cannot succeed without them (Benson (from Regular Show) is heavily trusted with keeping the park afloat, and SpongeBob SquarePants is very capable in doing his job as the fry cook of the Krusty Krab.)
3. Characters preventing catastrophes including end of the world or universe with their mere presence or actions (One-Above-All (Marvel Comics) keep the Marvel universe running, preventing it from disaster and Primus keeps the very fabric of the Transformers' reality from ripping.)
4. Some anti-heroes (Kratos (debatably), The Punisher, and The Hero of Bowerstone)
5. Major Good vs. Evil scenarios where one of the characters from the good side is the only subject that was strong/powerful enough to defeat the most dangerous evil (Naruto Uzumaki was the only person who could enhance powerful ninjutsu and techniques to defeat Nagato's Six Paths of Pain; Master Po (from the Kung Fu Panda franchise) was the only one who could stop Tai Lung, who was about to kill Master Shifu; the Hulk was the only one who could stop the Abomination in the 2008 adaptation of The Incredible Hulk; Avatar Aang was the only one who was very powerful enough to defeat the Phoenix King Ozai; and Raven (from the 2003 animated adaptation of Teen Titans) was the only Titan who could enhance her dark powers to destroy her demonic father, Trigon, and restore the city.)
6. Business Heroes that can provide a product, service or even information that is needed or well liked by people (Mr. Krabs runs the Krusty Krab which produces the very well-accepted Krabby Patty, and Nick Fury is in charge of S.H.I.E.L.D., an organization that have access to an extensive array of cutting edge technology, including some of the most advanced weapons and equipment available.)
7. Heroes performing actions that lead to beneficial results (Professor Utonium accidentally spilling Chemical X into his concoction for perfect little girls (courtesy of Jojo, his monkey) leading to the creation of the female superhero team called the Powerpuff Girls; Morpheus finding and testing the former redpill named Thomas A. Anderson, leading the latter to become Neo; Captain America fought the Red Skull during the World War II, leading to the revival of The Avengers; and Master Splinter named the four turtles Leonardo, Donatello, Raphael, and Michelangelo (after a book on Renaissance artists that he found in a storm drain) and trained them in the arts of ninjutsu, leading the main heroes to grow more powerful and reliable to take on any threats over the course of the series.)
8. Good Rulers or Officials that helped the place they live in (such as Tsunade helps keep the city of Konohagakure afloat.)
9. Amoral entities that must keep the balance of nature in check (Almost every incarnation of any type of God in mythology is this)
10. Family Breadwinners (Hank Hill, Al Bundy, Homer Simpson and Peter Griffin are often the only people in the family that actually work to put food on the table)
11. Successful Anti-Villains (Lelouch vi Britannia purposely made himself an potential threat of the world so the world would unite against him and temporarily create peace.)
12. Many mentors that train the heroes so they would grow stronger to defeat a greatest threat (Erwin Smith, Master Fung and Kakashi Hatake are the best examples of this)
13. Some fallen heroes (When Harvey Dent helped locked half of Gotham's crime bosses away in The Dark Knight, he gave hope to Gotham. When he became Two-Face and killed some people, Gordon and Batman knew if the truth came out, people would lose hope so Batman willingly took the blame so Dent would stay a hero after his death)
14. Any characters of Lawful alignment, law enforcers or cops who keep order (Judge Dredd, Joe Swanson and Lin Beifong are known to keep peace and order in their respective home cities)
15. Some biological species, tribes, or civilizations that while hostile or xenophobic, are capable of producing children and families. Killing of a naturally hostile race, civilization or tribe would still be considered an act of genocide (The Predators)
16. Certain Teachers who keep unruly students in line (Ms. Finster and Principal Peter Prickly from Disney's Recess are the good examples of this.)
17. Certain Powerful Alter-Egos within a hero, the ones that has possessed the hero, or grant them their powers resulting in them saving his/her lives from time to time. (Kurama sometimes possesses Naruto, or give some of his power to prevent Naruto from getting killed or to fight off a powerful foe, and Yami-Yugi frequently helps Yugi out.)
18. Redeemed Villains that joined, or at the very least, helped the good guys (Piccolo Jr., Yasha and Zuko are the good examples of this.)
19. Several Supporting Characters that aid a protagonist(s) on their quest, attempt to sacrifice themselves to save a protagonist(s), or sacrificed their lives to save the protagonist(s) or their homeland: such as Android 16, who attempted to self-destruct to kill Cell and Terra (from the 2003 version of Teen Titans), who sacrificed her life to save the city from an erupting volcano (who also qualify for "Redeemed Villains" above)