EXCLUSIVE

Robert Downey, Jr.'s "Iron Man" suit was a shameless copy, kind of like a designer ripping off a Vera Wang wedding dress ... so claim 2 guys who now say Marvel and Disney jacked their suit.

Artists Ben and Ray Lai claim in a new lawsuit they came up with a design in 2001 depicting a "futuristic, armored, and weaponized" body suit and featured it in their "Radix" comic book.

The following year they say Marvel hired them to work on various comics.

The Lai's point out ... the original "Iron Man" suits from the comics -- created in 1963 -- were simple spandex that had minimal armor. But fast forward to 2008, when the first "Iron Man" movie was released ... they say Robert Downey. Jr.'s suit was a dead ringer for theirs.

And they say to add insult to injury, Marvel used almost the exact same pose from their book for the "Iron Man" 2 and 3 posters.