After repeatedly setting new all-time highs so far in 2013, shares of Disney (DIS -0.04%) seem absolutely unstoppable. In fact, as of this writing, the entertainment giant's 27% year-to-date return stands second in the Dow Jones Industrial Average only to Hewlett-Packard's stellar 43% rise.

Owners of Disney stock can largely thank the release of Iron Man 3 for their most recent gains. As fellow fool Tim Beyers pointed out, the movie already earned $195.3 million overseas during its opening weekend, beating the already massive international opening achieved by The Avengers last summer by about $10 million.

Disney stock, Iron Man 3

Iron Man 3 screenshot. Source: Marvel.com.

Coupled with the fact that Iron Man 3 was only released yesterday in China and Germany, today in Russia, and opens tomorrow in Canada and the U.S., it's safe to say that its early success bodes well for both Disney and its stockholders.

Of course, the House of Mouse has already started building excitement with the release of its first trailer for Thor: The Dark World a little over a week ago. While this one certainly isn't expected to garner the same amount of attention as Iron Man, Thor's introductory film did manage to rake in nearly $450 million worldwide at the box office last time around, including a respectable $66 million on opening weekend.

Marvel fans can also look forward to seeing more of the good ol' Cap with Disney's planned release of Captain America: The Winter Soldier in April 2014. And let's not forget any future installments of The Avengers -- the second film is reportedly already in development -- or The Incredible Hulk.

The first 9,000
So how long can Disney keep this up?

According to Marvel, there are no fewer than 9,000 distinct characters in the Marvel universe. That's not to say every one of those superheros would be perfect to star in his or her very own movie, but you can bet that Marvel Studios has more than enough material to keep us entertained for ... well ... longer than the lifespan of us regular folk.

Marvel Universe, Disney stock

Image source: Marvel.com.

We can also keep in mind that Disney doesn't currently own the rights to every character in the Marvel universe. News Corp. subsidiary 21st Century Fox owns the rights to the X-Men and Fantastic Four, and Sony has proven adept at milking every ounce of its claim to Spiderman -- but remember, according to the comic books, both Spiderman and Wolverine should technically be a part of the Avengers team. As long as those studios finish at least one movie for each franchise every few years, however, those rights won't fall back into the waiting hands of Disney and Marvel.

Incidentally, that's exactly how 21st Century Fox lost the rights to Daredevil just a few days ago, giving Marvel one more tool in its belt to use down the road.

So what else do the folks at Disney and Marvel Studios have in store? As it turns out, at last year's Comic-Con in San Diego, they showed some of the first test footage for Ant Man (trust me, it's cooler than it sounds), and revealed concept artwork for their upcoming Guardians of the Galaxy movie, tentatively planned for release in August 2014.

Guardians of the Galaxy, Disney stock

Guardians of the Galaxy concept artwork. Source: Marvel.com.

Now, before you go rolling your eyes, remember how few people really cared about Iron Man and Thor before decent CGI finally brought them to life on the big screen.

The other 17,000
So where did I come up with the 26,000 in the headline? Look no further than Disney's $4 billion acquisition of Star Wars creator Lucasfilm late last year.

Source: Starwars.com.

As I noted at the time, in addition to a 2015 release of Star Wars Episode VII, Disney also told elated Jedi fans they're hard at work on two other character-specific Star Wars movies for release after Episode VII. Even more impressive than Marvel, however, are the 17,000 individual characters belonging to the Star Wars universe.

The bigger question
Now that we've established that Disney has at least 26,000 characters to work with from the Marvel and Lucasfilm acquisitions alone, a bigger question remains: How long will audiences continue to eat up everything these properties have to offer?

My answer? Indefinitely.

After all, superheroes, as we know them, have existed at least since the 1930s. For instance, Superman -- a Time Warner property, mind you -- made his first comic book appearance in 1938. While he continues to evolve, the world is certainly still excited about the guy with the blue tights and red cape.

And when graphics technology inevitably makes today's movies look ridiculously unrealistic (have you watched News Corp.'s first X-Men movie from way back in 2000 recently?), Disney will happily reboot their Marvel and Lucasfilm franchises to appeal to new generations of adoring fans. In the end, when you add to the mix Disney's ownership of Pixar, along with its theme parks and television networks, it's hard to envision a scenario in which Disney stock fails to outperform the market.