In recent years, the Disney-owned company has taken several steps to introduce greater racial and gender diversity: in 2014, a black man became Captain America and Thor became a woman. The year before that, Marvel introduced Kamala Khan, a Muslim teenager, as the super-hero Ms. Marvel.
One reason for increasing character diversity is to expand Marvel's audience, according to Augie De Blieck Jr., a columnist at Comic Book Resources.
"Marvel has relied on an ever-dwindling population to market its books to. Overwhelmingly, that's white men now in their 30s and 40s, who were reading comics during the last comic booms," he told CNBC via email.
"They need new people to market their comics to. With the boom in movie and television superheroes, there's an audience out there that craves this superhero material now. Those people aren't always being marketed to, like children, women, and insert your favorite ethnic minority in the United States here."