Once more, Iron Man has proved invincible at the box office. Iron Man 3 opened to $175.3 million in U.S theaters this weekend, second all-time to Marvel's The Avengers.

Reviews are mostly strong for the film that kicks off "Phase 2" of Walt Disney's (NYSE:DIS) plan to bring thousands of Marvel Comics characters to life on the Big Screen.

That's the good news. The bad? We don't know if Robert Downey Jr. will be a part of the plan going forward. Neither the actor nor his representatives say whether he'll reprise the role of the man underneath the helmet: billionaire industrialist Tony Stark.

Disney needs Downey in the role. There's too much at stake to not re-sign him.

And now playing the troubled genius ... the troubled genius!
Critics are likely to agree. Most praise Downey's work throughout the series. And me? I've been a fan since the beginning, praising Marvel's choice of Downey over Tom Cruise six and a half years ago when others were still unsure.  Here's what I said at the time:

Enter Robert Downey Jr., who, as of yesterday, landed the role. Plagued by many of his own high-profile troubles, Downey remains one of my favorite actors, and a perfect choice to play Stark. Seriously, who better to play a troubled genius than ... a troubled genius, as Downey surely is?

Hi Res Domestic Poster Iron Man

Source: Marvel Entertainment.

Fast-forward to today. The "Iron Man" franchise is already responsible for more than $3 billion in gross box office receipts worldwide if you include The Avengers, proving once again that CEO Bob Iger effectively stole Marvel when he arranged for Disney to pay just $4 billion to acquire the comic book company.

Too much source material, too many unanswered questions
Now that Iron Man 3 is a financial success, fans and observers alike are wondering if Downey will be back to headline Joss Whedon's Avengers 2 and perhaps another slate of Iron Man films.

Count me among the curious, and not just for financial reasons. While my colleagues spent the weekend tracking Warren Buffett's every move at the Berkshire Hathaway annual meeting, I took in two showings of Iron Man 3: once at a late Thursday screening with my fellow nerds, and then yesterday with my sons.

Fun fact: I pitched Marvel as a Berkshire-worthy value buy 10 months before Disney's big bid. I'm available for portfolio management services should you require them, Mr. Buffett.

I'll not spoil Iron Man 3 for you if you haven't yet seen it. Instead, I'll say that I think the ratings drop from 94% to about 80% at Rotten Tomatoes is probably justified. I also find myself wondering if Time Warner's (NYSE:TWX) Superman reboot, Man of Steel, will outdo IM3 to claim the box office crown among this year's crop of comic book films.

Go ahead, cue the Ozzy
For me, Iron Man 3 leaves a lot of questions unanswered, as it borrows heavily from a more recent plotline in the comics. Decades of source material remain unexplored. Meanwhile, Marvel is creating its own "Cinematic Universe" that strings together films as if they were part of an ongoing comic book series. Actor continuity will aid the effort, yet that's anything but assured at this point.

All we have are clues as to Downey's return. For example, there is a moment in Iron Man 3 when, in a nod to the closing of 2008's Iron Man, Downey once more says "I am Iron Man" to the delight of many in the audiences I was with. The closing credits also say, "Tony Stark will return."

Source: Marvel Entertainment; YouTube.

Disney and Marvel want Iron Man to be a multibillion-dollar franchise in the way that Harry Potter was for Warner and Transformers still is for Viacom (NASDAQ:VIA) and licensor Hasbro (NASDAQ:HAS), which means it can't end with Avengers 2. There has to be an Iron Man 4, and Robert Downey Jr. has to star in it.

Do you agree? Please vote in the following poll, and then leave leave a comment to let us know what you think of Disney's handling of its Marvel Comics properties.

Fool contributor Tim Beyers is a member of the Motley Fool Rule Breakers stock-picking team and the Motley Fool Supernova Odyssey I mission. He owned shares of Time Warner and Walt Disney at the time of publication. Check out Tim's Web home and portfolio holdings, or connect with him on Google+Tumblr, or Twitter, where he goes by @milehighfool. You can also get his insights delivered directly to your RSS reader.

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