Ttyjukl

Thor is a pretty tough guy. In the Marvel Cinematic Universe, Thor frequently appears to be the strongest among the Avengers (managing to bust up Iron Man's suit without breaking a sweat). That makes sense - humans are always pretty lame compared to superheroes.

However, Thor seems to be even stronger than the average Asgardian - as evidenced in both of his eponymous movies where he single-handedly defeats hordes of Frost Giants and Dark Elves. This too is hardly unexpected, as he's the heir to the throne of Asgard, son of the Allfather, and wielder of Mjolnir. But still, I find myself asking... why?

Is he genetically superior in some way? Did he eat more of the Apples of Idunn than his peers? Does the Allfather's magic run through his veins, granting him greater abilities than a footsoldier of Asgard?

As a note of curiosity, his pals in the movies (the only other heroes who get names at all) who accompany him on his many misadventures to the Nine Realms seem to be better than average as well. Sure, this could be chalked up to "they're protaganists, get over it" - but I'd like a better explanation.

How strong are Asgardians? discusses Asgardians' strengths in general, but only briefly mentions Thor specifically. I'd prefer an in-MCU answer if possible.

You are right in thinking that Thor appears to be stronger than any other Asgardian, but it has nothing to do with him as a person.

You've already mentioned the reason for his strength in your question, but you appear to be mistaken about the link they share. Thor isn't strong and as such he is allowed to wield Mjölnir, Thor is strong because he wields Mjölnir.

This magical extremely advanced technological hammer was forged in the heart of a dying star, granted to Thor by Odin (his father) and can only be wielded by those it considers worthy. An inscription on the side of it reads;

"Whosoever holds this hammer, if he be worthy, shall possess the power of Thor."

It is this that gives Thor the strength and durability that makes him stand out even amongst Asgardians, and we have seen in Thor that when considered unworthy, he loses his powers until proves himself worthy once more.

As for his friends Sif, Volstagg, Fandral and Hogun (known collectively as Lady Sif and the Warriors Three), they just happen to be some of the best warriors that Asgard has to offer. They are simply extraordinary Asgardians, which is likely the reason that Thor, who by his own admission courted war in his youth, was drawn to them in the first place. Unfortunately, we do not know much about these characters back stories within the Marvel Cinematic Universe as the films have (naturally) been more about Thor than they have his supporting cast.

It is also worth mentioning that in the Marvel Cinematic Universe, we have seen no evidence of the Apples of Idunn that give the Asgardians immortality in the comics. It seems to me that the Marvel Cinematic Universe seems to be pushing more towards the advanced aliens concept than the comics do, with Asgardians being mortal (albeit with extremely long natural lives) and with some of their technology being recognised as technology rather than being mistaken for magic by Jane Foster in Thor: The Dark World.

With the release of Thor: Ragnarok, aspects of Dr R Dizzle's answer have now been invalidated. In particular:

Thor's hammer is destroyed, and yet he still retains his Asgardian strength/durability/physiology.

This seems to indicate that his standard Asgardian powers are his again, and not imbued by the hammer. We never see him depowered without the hammer since the first movie, so it's hard to say when the enchantment was no longer in effect.

Furthermore, we get a clearer answer to the original question:

After Odin dies, he reappears to Thor near the end in a vision, explaining that the hammer was a tool to help him control his true power as the god of thunder ("What are you, Thor, god of hammers?" - Odin). We are also shown that Hela, Odin's daughter, once wielded the hammer. Even without it she likewise had formidable powers, enough to take on all of Asgard herself.

From this we see that Thor is not merely an Asgardian, and does in fact have special powers/abilities tied to his lineage as a royal of Asgard. But whether it be genetic, technological, magical, or something in between that is "The Odinforce", we do not know.

@Thomas we do see Frigga conjure an illusion of Jane Foster in The Dark World just before being killed, so believing she had trained Loki in this art is not a far reach.

I'm inclined to believe that this "magic" is in some way related to whatever force Dr. Strange taps, albeit on a more limited basis. It seems likely that only the royal Asgardian bloodline (the exception being the adopted Loki) would be granted access to that particular training. On a side note, we also saw in Thor: Ragnarok that it was the force of Odin's life that somehow kept Hella incarcerated in some other realm. Again, this seems like Dr. Strange-level power.