>>149044518
in 1972, National, by then owned by Warner Bros which at the time was owned by the mob, leased the rights to the old Fawcett catalog and started production of a tv show, and sued Marvel Comics over their by now popular and well-established Captain Marvel; National soon discovered that they had no naming rights precisely because they'd sued Fawcett into oblivion 20 years earlier
in 1974, Warner Bros/National made the show but called it Shazam!; it ran for two years and three seasons, eventually spinning off into The Secrets of Isis, about a character called Isis (after the Egyptian goddess, not the as-yet-unborn terror state)
in 1975 or 1977 (or whenever), National finally bought the Fawcett back catalog (instead of leasing the rights)
both the show and National's comics (which became DC Comics in 1977, but had been informally known as DC for some years before that) used Captain Marvel's name for the character by agreement with Marvel, whose EiC/Publisher (Stan Lee) and various staffers all thought highly of the Fawcett character (their own Captain Marvel's powers are an homage to the original, as is his swapping with Rick Jones) and felt the Fawcett creatives had been given a real shafting by National in the 1950s (they had); DC is technically allowed to use the character name but has chosen Shazam as this is the name they use for the show, movies and comics, because they lack the trademark and thus the right to trade under that name (sell things named "Captain Marvel"); this is entirely DC's fault, not Marvel's, and the modern character has little in common with the Fawcett version
the show by the way was a cheaply-made disaster area - midway through season 2 they fired and replaced their Captain Marvel actor because he didn't turn up for work; this was because he was at the doctor seeking treatment for an eye injury he'd sustained doing stunts on set the previous day; they ended up paying him for the full run of the show, in addition to the new guy