"The Coming of Captain Marvel" was a long development at the newly dubbed "House of Ideas". Of course the original Captain Marvel was the "Big Red Cheese" from Fawcett Comics, the hero who had fallen both to slipping sales and courtroom pressure from DC Comics.
The character and the name had become merely a part of comics lore, a beloved character by those who had seen the adventures, but little known by newer fans brought into the hobby by the success of Marvel Comics. It seemed a natural for a company named "Marvel" to have a Captain named "Marvel". And so it was, but before that came the Captain Marvel from Myron Fass.
This peculiar superhero was created by Carl Burgos, a man who had good reason to want to stick to Martin Goodman and the folks at Marvel since he had been recently denied in court his rights to the Human Torch. Like the latter hero, this new Captain Marvel was an android, one could divide his body into parts for whatever good that did him. It didn't bring sales and he soon disappeared, and there was likely mention that Marvel might take action too.
That left the door open for a new Captain Marvel and Goodman wanted that opening occupied posthaste and so we get the hero of the Kree, the conflicted Captain Mar-Vell.
Quickly cobbled together, Stan tapped Gene "The Dean" Colan and inker Frank Giacoia to draw a story of Kree. After the defeat of both Sentry 459 and Ronan the Accuser in the pages of Fantastic Four, the Kree send a starship to investigate and to monitor the "backwater" planet Earth which has been causing so much trouble.
To that end they dispatch Captain Mar-Vell, a young Kree Captain to operate on Earth undercover while his superior officer Commander Yon-Rogg observes from a safe distance in Earth orbit. Also aboard the ship is Medic Una, the girlfriend of Mar-Vell and a woman Yon-Rogg has designs on.
In Marvel Super-Heroes #13 the good Captain continues his mission. In this installment written by Roy Thomas we immediately get some changes in the premise established in the debut. For one thing because of Yon-Rogg's interference a small plane crashes and its single occupant is killed. That man named Walter Lawson proves to be a rocket scientist and Mar-Vell quickly capitalizes on this by assuming Lawson's identity and infiltrating the rocket base called "The Cape". He immediately (and most appropriately) comes under the suspicious eye of security chief Carol Danvers.
Despite amazing holes in his story, Lawson somehow convinces the authorities he's legit and gains access to the base. But he soon learns the Cape has recently come into possession of a great prize, an inert robot found in the depths of the Pacific Ocean. It is in fact Sentry 459, the same one defeated by the Fantastic Four. Seeing a chance to cause Mar-Vell trouble and perhaps even kill him, Yon-Rogg reactivates the Sentry who appears to have grown to thirty feet and he begins to ravage the Cape. Captain Mar-Vell gets into uniform and confronts the deadly emissary of his own people.
And that's that. There was supposedly going to be a third Captain Marvel story in the next issue of Marvel Super-Heroes, but the decision was made to give the Captain his own comic. We'll take a look at that next time.