Captain Britain first appeared in 1976, with an origin story that reads like a mash-up of Captain America, Doctor Strange, Spider-Man, and The Santa Clause. Whilst interning at a shady energy research facility, physics student Brian Braddock witnesses a group of armed mercenaries take over the facility, and so rides away to get help. On the way, however, he's involved in a terrible accident that leaves him at death's door...at which point Merlin, of Arthurian legend, appears and offers to heal him on the condition that Braddock becomes the defender of the British Isles forever.
So what makes this property the next big thing? Well, the MCU is probably going to need a replacement for Captain America considering that Chris Evans is leaving the franchise after Infinity War Part 2: Electric Boogaoverused Joke Sequel Name, and who better? Not only does he have the whole "Captain" thing going on, Captain Britain is imbued with superstrength, an energy field that protects him from harm, and the ability to fly, alongside the average, run-of-the-mill superintelligence that every Marvel protagonist has. He's Captain America v2.0, and he even comes complete with his own nemesis, in the form of the European Union.