Inhumans are no strangers to the Marvel Cinematic Universe. As a matter of fact, they've been around for a quite a while now, having been introduced in the second season of "Agents of S.H.I.E.L.D." However, up to this point, the Inhumans that have appeared on the show were created specifically for the series, with the exception of one Miss Daisy Johnson -- but all that's about to change.
"We do have a little more freedom," executive producer Jed Whedon revealed at Comic-Con International in San Diego. "We've told a couple of seasons of stories but now we do have some more freedom. So when we return to focusing on Inhumans, we'll be able to do a little bit more." According to io9, Whedon and Tancharoen specifically mentioned that they will be able to use some of the classic Inhumans moving forward.
It seems neither Whedon nor Tancharoen offered any insight into who these "classic Inhumans" are, but they're likely referring to the Inhuman royal family, who first appeared as a backup story in Stan Lee and Jack Kirby's "Fantastic Four" #45. Though the Inhumans encompasses an entire race of genetically engineered Kree-human hybrids, these stories focused largely on the aforementioned royal family, which includes Black Bolt, the king whose voice could level cities; Medusa, his wife, who possesses prehensile hair; Crystal, her element-controlling sister; Gorgon, a cousin who generates earthquakes with a single stomp; and Karnak, another cousin, who can pinpoint the weakness in anything.