Following a trial in which DC Comics sued Fawcett Comics for breach of copyright, claiming Fawcett's Captain Marvel was too similar to Superman, the latter stopped publishing Captain Marvel in 1953.
In the late 1960s Marvel gained the trademark "Captain Marvel" with its first series. In order to retain its trademark, Marvel has published a Captain Marvel title periodically every few years since, leading to a number of ongoing series, limited series, and one-shots featuring a range of characters using the Captain Marvel alias.
The first Captain Marvel is Mar-Vell. Created by Stan Lee and artist Gene Colan, the character first appeared in Marvel Super-Heroes #12 (December 1967).
Captain Mar-Vell is an alien military officer of the Kree Imperial Militia sent to observe the planet Earth, as it is developing technology to travel into space. Mar-Vell eventually wearies of his superiors' malicious intent and allies himself with Earth, and the Kree Empire brands him a traitor. From then on, Mar-Vell fights to protect Earth from all threats. He was later revamped by Roy Thomas and Gil Kane.
Having been exiled to the Negative Zone by the Supreme Intelligence, the only way Mar-Vell can temporarily escape is to exchange atoms with Rick Jones by means of special wristbands called Nega-Bands. He is also given superpowers, and his Kree military uniform is replaced with a form-fitting costume.
The process of the young man being replaced in a flash by the older superhero was a nod to the original Fawcett Captain Marvel, which had young Billy Batson say the magic word "Shazam" to transform into the hero.