Body armor has been around for centuries (made of bone, wood, silk and various metals). Knights in shining armor may come from a chauvanistic past (that’s an intended pun), but they still invoke visions of mighty warriors fighting for justice (even misguided justice).
Using science in the service of justice is also an old trope; many golden age SF tales are themed around just such a concept.
It’s therefore not a surprise to find numerous examples of modern knights featured in our tales. On the other hand, flying armored knights are probably unique to science fiction.
Robert Heinlein’s Mobile Infantry troopers didn’t fly so much as bounce. His YA Starship Troopers novel was released in 1959 and would seem to be the modern progenitor of this trope, as well as probably inspiration for Marvel’s Iron Man. Might seem, that is, until we remember the Republic Serial from 1949 – King of the Rocketmen.
Republic studios is famed for their cliff-hanging, action-adventure serials, which often played in theaters prior to the main feature (theater owners loved them because they kept movie goers coming back for next episodes); among their more famous productions are Dick Tracy, the Lone Ranger, Jungle Girl, Captain Marvel, Captain America, Zorro, and more. (Including numerous science fiction and fantasy serials).
King of the Rocketmen featured a Science Association targeted for murder and destruction by “Dr. Vulcan” in a bid to take over the world. Two surviving scientists create a nuclear powered jetpack and use it to thwart the Vulcan’s plans.
This serial play of 12 chapters was edited down to become the feature film Lost Planet Airmen.
If you compare the initial look of the rocket suit and the first take on Iron Man from Tales of Suspense, you’ll see that there’s a remarkable resemblance:
But I do have to say, from a personal perspective, that the Rocketman’s controls (yes, an inspiration for the Rocketeer – see?) 
are absolutely hilarious. It seriously makes me wonder what the prop department at Republic was doing the day they came up with it:
While studying it reveals that it is absolutely ludicrous, it does have the virtue of being easily replicated by an inspired kid, armed with only a pair of scissors, a carboard box and some crayons…. (one does wonder how different degrees of On and Off affect the Speed….)
Regardless, King of the Rocketmen got made into Lost Planet Airmen and here it is (sans accompaniment by Commander Cody)
