He has yet to be inserted into the Marvel Cinematic Universe, but Marvel has been alluding to Richard "Nova" Rider's debut since Guardians of the Galaxy (2014).
Intergalactic superhero Nova has yet to step on screen in the MCU despite his origin story slowly coming together even before Avengers: Infinity War (2018). The title of "Nova" has been passed from hero to hero through the pages of Marvel Comics, the first iteration of Nova, Richard Rider, was teased in James Gunn's first Guardians.
Rider's backstory, penned into The Man Called Nova #1 (1976), depicted Rider as a New York high schooler who is connected to Rhomman Dey through the cosmos. Dey, a member of Nova Corps, sought out Rider to bestow his powers onto him before his death. Rider, now as Dey's successor, takes on the role of the leader of the Nova Corps and heads for the planet Xandar that he will now call home.
For some fans, it was perceived that Rider would enter the scene as Nova after Xandar was destroyed by Thanos in order to possess the Power Stone in Infinity War. Because the destruction of Xandar was not seen, this means that the anticipated character still has room to weasel his way into the MCU. Though it could be said that Rider's origins were found during Infinity War, there's still a bit more backstory that can support Nova's eventual role in the MCU.
Dey's introduction in Guardians of the Galaxy has a more prominent tie to Rider. In Gunn's Marvel directorial debut, Dey (John C. Reilly) and Irani Rael (Glenn Close) are the prime representatives of Nova Corp. The duo was essential to defending Xandar from Ronan the Accuser (Lee Pace), a Kree warlord whose alliance with Thanos has hellbent him over havoc and destruction, seeking out the Power Stone. Guardians closes on the defeat of Ronan before passing the Power Stone along to Nova Corp for its protection.
They may have not been taking center stage in this intergalactic hero film but without the involvement of Nova Corp, there would have been no meaning behind Xandar's decimation. Guardians established both Nova Corp and their home planet, so that if (and when) Rider accepts his fate as Nova, the foundation of his backstory would stand firm.