In the Marvel Universe, I would be most impressed if I asked which character had appeared. I wouldn't choose mainstream superheroes, instead, I would choose a Winterfighter played by Sebastian Stan.

Bucky, played by Sebastian Stein, first appeared in the first film of Captain America in 2011, when he appeared as Steve Rogers' childhood best friend. Although Bucky died in the first film, unsurprisingly, in Captain America 2, he returned to the film as a villain. Unconsciously, 10 years have passed since the debut of the Winter Warrior.
As an Assassin frolicked by Hydra, The Winter Warrior made many mistakes, including murdering Iron Man's parents. Fortunately, Steve Rogers has impressed his former friends through his friendship. In Marvel's future films, the Winter Warriors are on the side of justice. He even owns the TV series Falcon and the Winter Soldier. In the play, we get to know the obscure but beloved Bucky. Naturally, in addition to our fans, Sebastian Stan himself is also very fond of the character of the Winter Warrior. He even posted on his social media account to celebrate his important 10th anniversary.
The actor, on his social media account, said that "Bucky's life's journey is an understatement." He also thanked fans for their love and support over the past decade. I have to say that Bucky in the photo is simply too handsome! Unconsciously, 10 years have passed, and the Marvel universe has undergone earth-shaking changes. We said goodbye to many superheroes, including Bucky's best friend, Captain America, but for now, the Winter Soldier is expected to stay in the Marvel Universe. Marvel is said to be working on Captain America 4, which stars new Captain America Anthony McKay. I think the WinterFighters might become the new Captain America's best friend in the future. After all, in Falcon and the Winter Soldier, his collaboration with Anthony McKay was excellent.
It is worth mentioning that since the Marvel Universe has entered the fourth stage, looking back at the several stages between them, villains like The Winterfighter have become members of the Avengers, and I wonder if in the fourth stage, some members of the Avengers will become villains again, such as the Crimson Witch?
Looking ahead, the Winter Soldier can appear in future Captain America 4 movies, and he can also appear in future Avengers movies. Although Marvel did not have an "Avengers" movie in the fourth phase, this does not mean that Marvel will have a large team movie like "Reunion" in the future. And with Marvel's TV series earning well, winter warriors can appear in all corners of the Marvel universe.
Anyway, a full decade has passed, and one thing is clear: Sebastian Stein, the Winter Warrior, has become a key player in the Marvel Universe. And I really hope that the character of the Winter Warrior can continue to stay in the Marvel Universe. After all, the shape of the Winter Soldier is really too handsome in "Captain America 2", and I hope that Marvel will give him a cooler look if he lets the Winter Soldier appear again in the future.