Being a leader is a huge responsibility-- more so in the Marvel universe. Without these courageous, powerful souls, Earth would have easily fallen into the hands (or jaws) or cosmic-level baddies. In both the MCU and the Marvel comic books, there have been many leaders, but some among them are the cream of the crop, the very best the Earth has to offer.
These guys and gals are always up to the task, and what sets them apart from the regular characters in Marvel are their selflessness, wisdom, and experience. So, in times of crisis, these individuals are some of the few people that draw the line between victory and defeat. Whether they're assembling the Avengers or gathering an elite force of mutants, they've taken on the responsibility and they're worthy of it (unlike some). Here are some of Marvel's greatest and most powerful leaders ever.
10 NICK FURY
Nick Fury has gone through a couple of facelifts, but Samuel L. Jackson's interpretation is a big fan favorite. The enigmatic and deceptive one-eyed spymaster of S.H.I.E.L.D. is responsible for many of the metahuman machinations on Earth. While he does tend to be manipulative at times, the Earth would be in even more danger without Fury.
More often than not, Fury is the one who keeps S.H.I.E.L.D. intact, resisting threats both internal or external. Of course, he occasionally gets help from superheroes (and sometimes villains), but Fury's compassion for the hapless citizens of Earth has saved the planet more than once.
9 DOCTOR STRANGE
Stephen Strange, a.k.a. Doctor Strange, essentially moonlights as the Nick Fury of Earth when it comes to inter-dimensional dangers. Ever since becoming the Sorcerer Supreme, he has been tasked with keeping Earth (and sometimes even the universe) safe from the unseen and unknown enemies that lurk in other realms.
That is a thankless job and Strange does it perpetually. While that responsibility is something that was already set in stone even before Strange was born, let's not discount the fact that he still managed to fulfill all expectations and gained the loyalty and trust of his own sorcerer peers... well, most of them.
8 CAPTAIN MARVEL/CAROL DANVERS
At one point, Carol Danvers became renowned enough to be a leader of the Avengers, thanks to Tony Stark's incessant prodding in Mighty Avengers (2007). For the Air Force veteran, it was somewhat easy; such experience also made her a qualified candidate.
How did Danvers fare as the Avengers' leader? Her initial unstable combination of Sentry, Ares, Black Widow, Wasp, Iron Man and Wonder Man managed to defeat a resurrected Ultron on their "training run." This proved Danvers' capability as the leader of the Avengers, and she goes on to replicate similar feats in future comic books.
7 ODIN
Being King of Asgard is not all rainbows and bifrosts, it's also full of busywork. Especially when one has to manage two troublesome sons and an ever-looming threat of invasion. For Odin, Thor's father, these things are just the standard Tuesday.
Managing your whole kingdom in a different realm while raising a family is work fit for a god. Luckily, Odin has both the power and the experience to deal with such matters. He's also wise enough to know that Thor's brash tendencies were causing more trouble than good and proceeded to teach him an unforgettable lesson in humility. Without Odin, Thor wouldn't have been half the superhero he is.
6 BLACK BOLT
A leader who never wanted to lead usually makes for a good one, as they often don't lust after power. Black Bolt is one such metahuman (or Inhuman) in the Marvel universe. At the tender age of 20, he was compelled to take up the mantle of leadership for his own kind, despite his silent protests and reluctance.
Suffice to say, Black Bolt's rule was full of strife and challenges. The Inhumans were constantly in danger of being discovered by humans, his brother Maximus was always poised to usurp the throne, and he faced several revolts within his kingdom. Even so, Black Bolt powered through and turned the Inhumans into a faction instrumental in the defeat of various cosmic threats.
5 BLACK PANTHER
Like Black Bolt, T'Challa understood the challenges of keeping his kingdom "underground." T'Challa knew the dangers that Vibranium could introduce to the whole human race if it fell on the wrong hands and thus kept the tradition of his forefathers to seal Wakanda.
Beyond that, T'Challa has also laid his life on the line many times as an Avenger. At one point, he even faced God Emperor Doom with nothing but an Infinity Gauntlet, just to buy time for the superheroes of Earth to undo Doom's work. Without a doubt, T'Challa is a leader fit to be called a king, both within Wakanda and outside of it.
4 CAPTAIN AMERICA
Here he is, the star-spangled man with a plan. Captain America (Steve Rogers) went from punching criminals to hammering godly beings like Thanos, which is a huge step-up for a scrawny Brooklyn kid. Throughout his journey, Rogers has proven time and again that he has both the heart and the will to face such threats and even sacrifice himself for everyone.
As such, he's often the de facto leader of the Avengers, often serving as its most popular poster boy along with Tony Stark. He's such a great leader that it proved to be a major catastrophe when he was re-written as a Hydra sleeper agent-- a testament to the fact that his leadership will always shine, even in a villainous capacity!
3 IRON MAN
Speaking of Tony Stark, he might appear to be a shallow billionaire with self-destructive tendencies (which he was at first, let's be honest), but the MCU has proven once and for all that Iron Man will always take a bullet for anyone-- armored or not. In fact, half of the Avengers Initiative was his idea.
While it stemmed from his fear of external forces invading Earth, his concern for people is undeniable. Stark's ultimate sacrifice in the MCU has made him the current best Avenger ever (sorry Rogers) and he has since become a far cry from his comic book character's messy beginnings.
2 REED RICHARDS
When it comes to wisdom and intelligence, not many superheroes can match Reed Richards. The Fantastic Four leader has been responsible for thwarting several cosmic menaces that have continuously threatened Earth. However, Richards' compassion extends beyond his fellow humans; he even has enough rationality to understand that beings like Galactus are necessary "evils" of the universe, especially for keeping balance.
Hence, when the future of Earth or humanity is concerned, there's no better paragon than Reed Richards... except perhaps his children, who might have already surpassed him in terms of intelligence. Of course, when it comes to bravery, Richards has it in spades, especially when he defeated Doom in Secret Wars; after which he proceeded to responsibly repair the multiverse.
1 PROFESSOR X
Apart from being the best leader the X-Men ever had, Professor X (Charles Xavier) is also the best teacher in the Marvel universe. He's a man who leads by example and it's safe to say that without him, the mutants and humans would have spiraled into a war of extinction. Despite having one of the most powerful brains among mutants, Professor X has practiced commendable restraint.
While he may resort to military methods sometimes, especially when lives are at stake, Professor X's goal is to establish and maintain a peaceful society.