Avengers: Infinity War and Avengers: Endgame movie featured how all the superheroes from this universe united as one to fight Thanos and his army. The movie had those superheroes whom we have seen in the previous movies like Captain America, Iron Man, Thor, Black Widow, and others, but there are reports that a new superhero was supposed to make a debut in Endgame but now we are going to see him in the untitled Avengers 5 movie.
It was previously confirmed by Marvel Cinematic Universe's Cosmic's Jeremy Conrad that a new hero is all set to make his debut in Avengers 5. It was previously assumed that Marvel's Nova is going to get featured in Marvel's Phase 5 alongside Blade, The Fantastic Four, Mutants, and others.
In Marvel Comics, Nova is a member of the intergalactic police force known as the Nova Corps., for which he gained superhuman abilities including enhanced strength, flight and resistance to injuries just like other intergalactic superheroes. After the events shown in Infinity War, it would have made sense to see Nova appearing in the final battle against Thanos. But now, the character will make his debut in the forthcoming Phase 5.
Most recently, Avengers: Infinity War and Avengers: Endgame writers confirmed that Nova was indeed first considered for Marvel's Phase 4 and he would have made his debut in Endgame only. During the ComicBook.com interview with writers Christopher Markus and Stephen McFeely, they confirmed that Nova was indeed considered to appear in both Infinity War and Endgame.
Christopher Markus talked in detail about the character and how they thought of bringing it on board in IW and Endgame. They responded by saying the following:
"The Xandarian Worldmind was that after... it was almost going... In this conception, he would be the herald, not unlike the Hulk, who was actually standing in for the Silver Surfer, but that one member of the Nova Corps survived Thanos' attack. The Xandarian Worldmind would be the voice of Glenn Close because you had her, and why not? And that he would be Richard Rider, and he would come to earth."
Even though fans did not get to see Nova fighting beside Iron Man or Captain America, we are surely going to see him when Marvel will premiere Phase 5.