We have narrowed it down to 22 characters who have been introduced throughout the Marvel Cinematic Universe who weren't seen in Avengers: Infinity War, although some of whom were actually mentioned or talked about. The 22 we have picked out at least have a shot, we think, some greater than others, at returning in Avengers 4, for various reasons, while the Honorable Mentions seem less likely, although some may be back in stand alone sequels. Without further adieu, here are the 22 major Marvel Cinematic Universe characters who weren't featured in Avengers: Infinity War, starting with the two most obvious.
Given his contributions in Captain America: Civil War, many assumed that Ant-Man a.k.a. Scott Lang (Paul Rudd) would show up in Avengers: Infinity War, but that didn't happen. Black Widow did mention both Ant-Man and Hawkeye (Jeremy Renner) during one brief scene, stating they opted to stay with their families. It has been reported that Ant-Man and the Wasp (July 6) is set between Civil War and Infinity War, likely setting up Ant-Man's return in Avengers 4.
Since it was already established that Hawkeye has a wife (Linda Cardellini) and kids to take care of, it wasn't terribly surprising that he chose to sit out Avengers: Infinity War and protect them. Hawkeye has already been confirmed for Avengers 4, with his new haircut and outfit suggesting that his family was killed by Thanos' actions, which likely motivates this stoic archer to return to join the Earth's Mightiest Heroes.
The Wasp (Evangeline Lilly) is another character who has already been confirmed for Avengers 4, and we'll likely learn exactly what she was doing during Avengers: Infinity War during Ant-Man and the Wasp, which is said to overlap with the events of Infinity War. Given that this sequel brings back her long-lost mother Janet Van Dyne (Michelle Pfeiffer), it's understandable that she sat out this fight, but expect to see her back in action in Avengers 4.
While some expected either Ant-Man or The Wasp to show up in Avengers: Infinity War, most weren't likely expecting their mentor (and The Wasp's father) Hank Pym (Michael Douglas) to make an appearance. Since Ant-Man and The Wasp sat this one out though, it makes sense that Pym does too, but while Ant-Man and the Wasp are expected to surface in Avengers 4, I can't see much of a reason for Pym to show up. Then again, with how little we know about the Avengers 4 story, anything is possible.
After Secretary of State Thaddeus "Thunderbolt" Ross (William Hurt) made an unexpected return in 2016's Captain America: Civil War, and after it was confirmed he would return in Avengers: Infinity War, many wondered if his daughter, Betty Ross (Liv Tyler) was too far behind. While Betty still hasn't surfaced yet, she could be a character whose unexpected return adds some shock value to Avengers 4, like the surprise appearance of Red Skull in Infinity War. There has been no evidence (set photos, rumors, etc.), perhaps she could be brought in at the last minute to provide some assistance with The Hulk (Mark Ruffalo).
Emil Blonsky, a.k.a. The Abomination
While it's been 10 years since we've seen The Abomination in 2008's The Incredible Hulk, he has been referenced on ABC's Agents of S.H.I.E.L.D. in more recent years. It has been revealed a few times on the show that he has been locked up in custody at a facility known as The Vault in Alaska. A character like this would be a prime candidate for a surprise cameo, and if another epic battle with Thanos (Josh Brolin) is coming in Avengers 4, the rest of humanity may need some help from this massive creature.
If The Abomination returns, it's therefore possible that his creator, Samuel Sterns (Tim Blake Nelson) could return as well. Sterns is in fact still alive, and like Abomination, he's in S.H.I.E.L.D custody, but it isn't exactly known where he's being incarcerated at. Still, Sterns would likely not do too much good in any sort of fight, but if The Abomination is set free, perhaps Samuel Sterns will get to tag along for the ride.
Tony Stark's nemesis Justin Hammer (Sam Rockwell) hasn't been seen on the big screen since his MCU debut in Iron Man 2, when he was locked up for his villainous deeds, and in the final One-Shot short film All Hail the King. Hammer is still locked away at Seagate Prison, so, barring a daring prison break, the best chance we'd get to see Justin Hammer is if someone else was sent to Seagate during Avengers 4, and that seems unlikely.
Agent Phil Coulson
If I had to put any money on any character making a long-awaited return to the movie side of the MCU in Avengers 4, it would be Agent Phil Coulson (Clark Gregg). Coulson's death at the hands of Loki in The Avengers helped galvanize Earth's Mightiest Heroes and bring them together, and while fans know he's really been alive this whole time, on the ABC series Marvel's Agents of S.H.I.E.L.D., no one on the MCU movie side knows this. Coulson is already returning to the movie side in Captain Marvel, which is set in the 1990s, but it's possible this also segues into a present-day return of Coulson in Avengers 4, bringing this character back from the dead, as it were... or at least back fro Tahiti...
Avengers: Infinity War directors Anthony and Joe Russo confirmed in an interview shortly after Infinity War's release that Sif was among the casualties of Thanos wiping out half of existence. This makes her a prime candidate to return in some fashion (since the prevailing theory is that those who were disintegrated will be reanimated), especially because she wasn't featured in Thor: Ragnarok, due to scheduling conflicts with her NBC series Blindspot. Then again, it's possible that the Russos really aren't bluffing and everyone who disintegrated stays dead, although no one really believes that since it would torch plans for several sequels, but we'll see what happens.
Like Justin Hammer, Trevor Slattery was last seen in Seagate Prison, in the Marvel One-Shot All the King's Men, but the ending of that short film made it clear that he was being taken to the real villain known as the Mandarin, who Slattery was pretending to be in Iron Man 3. Slattery is one of the few characters in all of the MCU whose fate is completely uncertain. He may now be held captive by the real Mandarin, or he could have been killed for impersonating him. It's anybody's guess at this point, but if he does return in Avengers 4, it will undoubtedly be one of the biggest surprise returns of the movie.
President Matthew Ellis
We haven't seen President Ellis since 2013's Iron Man 3, and there may not be a better time to bring him back than in Avengers 4. After all, half the world's population was just blinked (or snapped, really) out of existence by Thanos, and it would certainly be interesting to see what the leader of the free world's thoughts on this world-altering event may be. Then again, so much time has passed between Iron Man 3 and now that it's possible he isn't even President any more, and Avengers 4 may introduce a new President of the United States. Still, it would be nice to bring Ellis back into the fold, even if he isn't he Commander-in-Chief anymore.
There have already been rumors that Harley Keener (Tye Sheridan) will actually return to the MCU in Avengers 4, following the youngster's memorable debut alongside Tony Stark (Robert Downey Jr.) in Iron Man 3. Keener was the young Tennessee native that Stark came across while trying to fix his suit. The actor was just 12 years of age when Iron Man 3 came out and he'll be approaching his 18th birthday when Avengers 4 hits theaters next year. It will be interesting to see how Keener's life has changed since that encounter with Tony Stark.
Sharon Carter/Agent 13
Agent 13, a.k.a. Sharon Carter (Emily VanCamp) is a character that I'm kind of surprised we haven't seen more of in the MCU, aside from her two appearances in Captain America: The Winter Soldier and Captain America: Civil War. Since many believe there could be a romantic connection between Sharon and Steve Rogers (Chris Evans), one possibility is that Steve and Sharon could both survive and end up living happily ever after as they both start a new life together, walking away from the trappings of the Avengers/superhero lifestyle. Still, even if this doesn't happen, it would be nice to see Sharon return in Avengers 4.
Corpsman Rhomann Dey
Corpsman Dey (John C. Reilly) only appeared in Guardians of the Galaxy, and given how Thanos destroyed Xandar to get the Power Stone, it's possible that he could be a casualty of Thanos' wrath, but that was never confirmed. Even if he is alive, there may not be much use for him in Avengers 4. Still, a Rhomann Dey cameo isn't entirely out of the question. It's possible that a grief-stricken Star-Lord (Chris Pratt) returns here to reflect on what he did. There is a subset of fans who "blame" Star-Lord for Thanos getting all of the Stones, and with a redemptive arc most likely coming, it's possible that if Star-Lord returns to assess the damage on Xandar, he runs into Rhomann Dey.
If Rhomann Dey does in fact return, it would make sense to bring back Nova Prime (Glenn Close) as well. The Power Stone was being kept at Nova Corps headquarters, and with Nova Prime as the current leader of Nova Corps, perhaps we'll learn more about how it all went down. Then again, there may not be much value to revisiting how one of the Infinity Stones was taken from Nova Corps on Xandar, but it would be a nice opportunity to bring Glenn Close's Nova Prime back into the franchise, although if it doesn't happen in Avengers 4, it may ultimately happen in Guardians of the Galaxy Vol. 3, which is confirmed for Marvel Phase 4.
We last saw this Ravager Kraglin (Sean Gunn) trying to perfect the usage of the Yaka Arrow in one of the Guardians of the Galaxy Vol. 2 post-credit scenes, and director James Gunn teased just after the release of Avengers: Infinity War, that Kraglin has some "important stuff" to do, which explains his absence in Infinity War It's certainly possible this "important stuff" will be revealed in Avengers 4, which he has long been rumored to appear in, but it still remains to be seen how his storyline will be integrated into the massive Avengers 4 plot.
Zemo (Daniel Bruhl) is one of the other MCU characters who is currently in custody, after having been arrested for his crimes at the end of Captain America: Civil War. While he was not seen in the flesh, he was mentioned in Black Panther and there was a photo shown of him, but there is still no concrete indication he could return in Avengers 4. Still, now that Bucky (Sebastian Stan) has been seemingly "cured" from all of the brainwashing he was subjected to years ago, which Zemo exploited in Civil War, it would be interesting to see Barnes, now known as The White Wolf, to come face to face with Zemo in Avengers 4.
Given that a major battle in Avengers: Infinity War takes place in Wakanda, and Avengers: Infinity War showcases almost all of the main characters from Black Panther, it's a bit surprising that Everett Ross (Martin Freeman) doesn't make an appearance in Avengers: Infinity War. Then again, if Zemo does return, it would be interesting to see him also react with Ross, the man who helped put him away. There is no indication yet that Ross will be featured in Avengers 4, but he could have an integral part in a few different story lines.
Since a lot of Avengers: Infinity War takes place on Earth, and not the Cosmos - practically the opposite of Thor: Ragnarok, most weren't surprised when The Grandmaster (Jeff Goldblum) didn't make an appearance, but don't be surprised if this colorful hedonist makes his return in Avengers 4. While there is no indication that any part of the Avengers 4 story will return to The Grandmaster's planet of Sakaar, it's worth noting that Thor (Chris Hemsworth) and the late Loki (Tom Hiddleston) did steal The Grandmaster's ship to escape Sakaar in, so perhaps The Grandmaster returns to try and get his ship back.
Korg, played by Thor: Ragnarok director Taika Waititi, was quite the surprise in Thor: Ragnarok, with the character stealing several scenes in a rather hilarious fashion. If The Grandmaster does set out in seek of his missing ship, then perhaps he will be accompanied by Korg, to provide some assistance, not to mention, comic relief. Since it seems unlikely that Avengers 4 will return to Sakaar, this hypothetical example could be one of the only possible scenarios that brings Korg into Avengers 4.
The exclusion of Nakia is perhaps one of the most surprising, since she did have a pivotal role in Black Panther and yet she wasn't seen in Avengers: Infinity War, while many other Wakandan characters were. She was last seen accompanying T'challa (Chadwick Boseman) to the United Nations, as they announced that Wakanda will finally share its resources and technology with the rest of the world. There is no indication yet that any part of Avengers 4 will be set in Wakanda, but if so, we should get another glimpse of Nakia.
The following characters are still, as far as we know, alive and well within the MCU, although it remains to be seen if they'll return in Avengers 4 or any other Phase 4 MCU movie: Christine Everhart (Leslie Bibb), General William Gabriel (Bill Smitrovich), Leonard (Ty Burrell), Cathleen Sparr (Christina Cabot), Howard Stark (John Slattery), Chess Roberts (Olivia Munn), Jane Foster (Natalie Portman), Erik Selvig (Stellan Skarsgard), Darcy Lewis (Kat Dennings), Richard (Chris O'Dowd), Howard the Duck (Seth Green), Laura Barton (Linda Cardellini), Dr. Helen Cho (Claudia Kim), Madame B (Julie Delpy), Paxton (Bobby Cannavale), Maggie Lang (Judy Greer), Cassie Lang (Abby Ryder Fortson), Luis (Michael Pena), Kurt (David Dastmalchian), Dave (T.I.), Aunt May (Marisa Tomei), Baron Mordo (Chiwetel Ejiofor), Christine Palmer (Rachel McAdams), Kaecilius (Mads Mikkelsen), Nicodemus West (Michael Stuhlbarg), Stakar Ogrod (Sylvester Stallone), Ego the Living Planet (Kurt Russell), Ayesha (Elizabeth Debicki), Taserface (Chris Sullivan), Tullk (Tommy Flanagan), Retch (Evan Jones), Gef (Steve Agee, Charlie-27 (Ving Rhames), Aleta Ogord (Michelle Yeoh), Mainframe (Miley Cyrus), Adrian Toomes (Michael Keaton), Michelle (Zendaya), Liz Toomes (Laura Harrier), Aaron Davis (Donald Glover), W'kabi (Daniel Kaluuya) and Ramonda (Angela Bassett).
Given the random nature of Thanos snapping his fingers and wiping out half the Earth's population, there is no surefire way of knowing whether or not any of these characters are really alive or dead, honorable mention or otherwise. Many have theorized that Thanos' actions will be reversed, whether it be by tracking down the Mad Titan and retrieving the Time Stone (a.k.a. The Eye of Agamotto), or through other means like the Quantum Realm. We'll find out who truly lives, dies, disintegrates or becomes resurrected in Avengers 4, slated for release on May 3, 2019.