Matt Fraction, the writer of " Invincible Iron Man " has explicitly stated in interviews that Tony Stark is indeed an atheist : The Iron Man story in Fear Itself, there’s a cataclysm that befalls one of Tony’s favorite cities in the world, and he goes to investigate it.
As the Avengers resources are split, and they’re running around the world dealing with Fear Itself, Tony goes to take care of this one thing.
It’s kind of an arc about science versus magic.
A man of science, an atheist, dealing with gods.
It really speaks to a lot of Tony’s greatest fears.
How deep does Tony’s faith in science go, and what happens when you shatter it on an anvil?
The ultimate man of science is forced to stare deep into the eyes of what can only be described as a god.
A god that wants to kill him.
And more recently they've actually referenced the image you've linked to...
He also expresses a deep mistrust of "gods" in older serials such as Iron Man #294
And in She Hullk #18, he explicitly identified his personal (non)religion; he's a "futurist":
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First of all; there is no proof about Tony Stark and his religious tendencies presented to us in the Marvel Cinematic Universe.
However, as a scientist with a skeptical mind, it is more likely than usual that Tony Stark is not a religious man and in this instance I believe that a lack of proof is more likely to mean he is an atheist, rather than a theist.
This is because he is a fictional character, and if an element of a character such as religion was important to them, it would be for a reason and be present in some form.
The fact that it isn't means we can certainly say that religion isn't important to Tony Stark in the writer's eyes, and as such probably not important to the character either.
It's also worth mentioning that the lifestyle that Tony Stark leads both pre and post-Iron Man is hardly one that a religious man would live.
He is a womanising, selfish, obnoxious and egotistical arms-dealer turned womanising, obnoxious and egotistical walking weapon.
That hardly screams religious to me.
That being said, the very nature of the picture you refer to is wrong.
Asgardians, at least in the Marvel Cinematic Universe, are categorically NOT gods.
It has been mentioned multiple times, from Thor to The Avengers/Avengers Assemble to Thor:
The Dark World that Asgardians are merely aliens with increased longevity, which has resulted in their culture progressing much slower than their technology, creating a world in which their advanced science is indistinguishable from magic to normal humans.
Additionally, even if Asgardians WERE gods, neither Captain America, Iron Man or the Hulk would have met two of them, as Loki is in fact a Frost Giant, not an Asgardian.
Which means that when Steve Rogers says; These is only one god ma'am, and he doesn't dress like that.
He's closer to the mark than it may appear.
Note: I appear to have created something of a... kerfuffle in the comments below regrading my answer.
In no way am I saying that intelligence and religion are mutually exclusive.
However, this article shows a solid correlation between American scientists and a non-theism when compared to members of the American general public.
As such, despite people's urge to find offence in what I have said, the likelihood of Tony Stark being an atheist is higher than that of the general population.
This, combined with all the other points mentioned above, speak volumes (at least to me) about Tony Starks religious tendencies.
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There is evidence in Age of Ultron that suggests Stark is an atheist (at least in as much as he does not believe in the Christian god).
Some Christians express their religious convictions by using a bumper sticker proclaiming the centrality of Jesus Christ in their lives: Here is a screen cap from the latest Avengers movie (roughly 13 minutes in), showing Stark's bumper sticker: Jarvis is the artificial intelligence that is often called upon to control Stark's machinery and provide assistance during times of difficulty.
Given the fact that Stark's Jarvis bumper sticker plays on the wording of the Christian Jesus bumper sticker, specifically replacing Jesus with an A.I., and that this might be considered blasphemous in the Christian religion, we can probably assume that Stark is, at least, not a believer in the Christian god, who tends to frown on this kind of thing.
Whether this means he does not believe in any god is a different matter.
He may consider Jarvis a deity, for example.
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Given that there's no evidence for Tony Stark's religious position within the MCU, it's actually entirely possible that his beliefs are undefined if the writers have never really thought about it as an important aspect of his character.
Writers frequently don't know anything about certain parts of their characters' lives because it just doesn't matter to the story they're trying to tell.
Of course, that in itself might mean he's an atheist of the non-evangelising variety - but there's no evidence of it.
We could appeal to the comics where he is definitely an atheist, but this is the MCU and we can't take anything from the comics as applying to it.
Therefore the only entirely correct answer is "we don't know".
We can assess that it's likely that he's an atheist, and I'd be surprised if they ever decided to contradict the comics on this, but really when there's no evidence in canon
you just can't say.
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Ultron makes multiple references to God and quotes at least once from the Christian Bible.
Vision speaks of "Grace.
" That's a weird thing for robots to do.
It's well established that Ultron has been copying Tony's speech pattern.
So it seems very likely that Tony occasionally uses religious language.
That vocabulary could just be assimilated from the people around him - I myself have used phrases like "oh my god."
But it's some evidence towards Tony being a Christian.
He's not Catholic - he makes a joke at their expense.
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I've seen an image multiple times on the Internet lately claiming that Captain America met two gods and still is a Christian (no doubt about this) while Tony Stark met two gods and is  still an atheist.   I'm assuming the image talks about Marvel Cinematic Universe's Iron Man. Is he really atheist? Do we have any hard evidence of this?
Is Tony Stark an atheist?
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<marvel><marvel-cinematic-universe><iron-man><religion>
scifi.stackexchange.com/questions/87436
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Matt Fraction, the writer of " Invincible Iron Man " has explicitly stated  in interviews  that Tony Stark  is indeed an atheist. However,  in She Hullk #18, Stark explicitly identified his personal (non)religion - he's a "futurist". Stark's AI bumper sticker is a play on a Jesus sticker, suggesting that he does not believe in a Christian God. Although there are many factors pointing towards Stark being an aetheist, most notably his Jarvis bumper sticker and his scientific background, there is no concrete evidence in the MCU to back up these theories, though the writer of Invinvible Iron Man has explicitly stated he is. Stark does, however, confirm in She Hulk that he is a futurist.
There is no concrete evidence in the MCU to confim Stark is an aetheist though his scientific background and his Jarvis bumper sticker may suggest that he is. In She Hulk, Stark confirms he is a futurist. The writer of Invincible Iron Man has publicly announced that Stark is an atheist.  