One of the most defining aspects of any art is that it is open to interpretation, and two people can indeed perceive the same piece of art in entirely different ways. 

But, what no one--the creator or the audience--can deny is that there has never been, and likely, never will be, a casting choice as perfect as Robert Downey Jr. for Iron Man. 

Robert Downey Jr. as Iron Man
Source: IndieWire

Fans of Marvel may say that Ryan Reynolds nailed the portrayal of the anti-hero, Deadpool. 

Ryan Reynold as Deadpool
Source: TIME

Fans of mutants would perhaps pick Hugh Jackman for his picture-perfect portrayal of Wolverine. 

Hugh Jackman as Wolverine
Source: the verge

Fans of magic and fantasies could choose Daniel-Emma-Rupert trio from the Harry Potter series. 

Harry Potter
Source: britannica

And while these are great choices, what everyone would agree on, is that only Robert Downey Jr. appears to have been born to play Iron Man. 

Robert Downey Jr.
Source: Geo TV

I mean, you don't just walk around life with that kind of charisma and style, while making even arrogance look appealing, for no reason. 

RDJ interview at comiccon
Source: YouTube

Though there are numerous instances that prove Tony Stark and RDJ are indeed one and the same, it's not just about how similar the character and the actor are.

RDJ car
Source: thethings

It's also about all that Robert Downey Jr. had brought to the character, seemingly with so much ease, that for millions of young fans (and a few older ones too) across the world, Robert Downey Jr. is indeed the Iron Man. 

RDJ
Source: Facebook

From gaining weight for the role, to pretending he was Iron Man even before the audition, Robert Downey jr. definitely 'methodeded' for the part. 

Additionally, whenever a movie has a novel or comic as source material, the director and actor are competing with the audience's preconceived notion of how a character should look like. Jared Leto, Jamie Dornan, Ben Affleck could probably tell a thing or two about this comparison. 

Jared Leto as Joker
Source: Hollywood Reporter

Competing with readers' imaginations is not a fair comparison by any means, and yet, Robert Downey Jr. won at it and how. 

RDJ with young fan
Source: Pinterest
RDJ with Fans
Source: EOnline

If I was the kind to believe in magic and destinies, I'd say Iron Man was Robert Downey Jr.'s destiny, much like it was Tony Stark's in the original comic. 

Iron Man 1
Source: Penn Today

Just as Tony Stark's darkest days led to the birth of Iron Man, Robert Downey Jr. also signed the first film at a point in his life when he could really do with a win. 

After suffering personal losses, and dealing with a drug problem, Robert made a comeback in 2001 and starred in movies like Gothika, Kiss Kiss Bang Bang, etc. 

Kiss Kiss Bang bang
Source: cinemablend

While he earned critical acclaim with his movies, it was the 2008 Iron Man that won him a blockbuster hit and the kind of adoration his talent truly deserved. 

RDJ as Iron Man
Source: Seattlepi
RDJ article
Source: LIST

Despite the fact that Robert wasn't Marvel's, or at that point anyone's, first choice for Iron Man, Robert Downey Jr. landed the role. 

Iron Man 1
Source: MentalFloss

As director Jon Favreau put it in an interview with the Texas radio station 100.3 Jack FM, 

By studying the Iron Man role and developing that script I realized that the character seemed to line-up with Robert in all the good and bad ways. And the story of Iron Man was really the story of Robert’s career.”
Favreau and Downey
Source: cinemablend

On the screen, he has been a billionaire, genius, playboy and philanthropist. And of course, a man in a suit of armor. 

Avengers Dialogue
Source: Pinterest

Off the screen, he has been an equally great philanthropist, a mentor to co-actors, a witty AF interviewee and an icon for kids and adults alike. 

And in all our hearts, he is the one and only Iron Man. No actor, no matter how talented, good-looking, or amazing, will ever be able to pull off the gold-and-red suit, and the persona that comes with it, as he did. 

Love you 3000, Mr. Stark aka RDJ.