A decade or so ago, the Marvel Cinematic Universe as we know it today was absolutely unheard of. Marvel themselves had no interest in making movies based on their own characters, which is precisely why they sold off so many properties for comparatively paltry fees. The films made by various other studios, such as Sony, 20th Century Fox, or Universal, ranged anywhere from phenomenal to god-awful.
Then, in 2008, something changed. Marvel took a risk and utilized one of the only characters they still had exclusive rights to - the so-called B-lister Iron Man - and decided that if you want something done right, you have to do it yourself. The gamble paid off and now, just under a decade later, the MCU has become one of the true juggernauts of the film industry, with Marvel setting their sights on the world of television as well.
One by one, they got the rights back to some of the characters they had short-sightedly sold off. While some were left untapped all that time, others had already been used by the other studios. Some were used rather poorly, with fans of each respective series losing all hope that their favourite characters would ever get their time in the spotlight again.
Fortunately, Marvel has gained so much traction that no matter how badly a character had been ruined by someone else, they could still make fans love them once more.