Everybody knows who Captain America is, but he is usually and underrated character compared to people like Superman or Thanos. Let me give you a heads up, he is much better than them, in fact he is the best superhero ever.
Created by Joe Simon and Jack Kirby first appearing in 1941 Captain America Comics, the first superhero ever created had been one of the oldest superheroes of all time. Over the years there have been many many people who have overtaken the role including Steve Rogers, Bucky Barnes, Jeffery Mace, the recent Sam Wilson and many others. Not only has there been many people who have filled in the roles but he has also inspired others to become superheroes such as the famous US Agent and Agent Venom. In fact in the Guardians of the Galaxy, a time displaced superhero named Major Victory wields the time displaced shield of Captain America.
The most famous Captain America is Steve Rogers. He is a skilled fighter, peak level of human condition, great commander, uses a vibranium steel alloy shield, and was given the super hero soldier serum. He can bench press a max of 1200 pounds. Not only is he skilled but he has wielded Thor's hammer Mjolnir and the godlike infinity gauntlet. He also wore the helmet of Richard Rider, Nova. When a normal person wears a helmet with such power they normally go mad or insane, but Steve showed the mental resilience and controlled the helmet. Cap is also one of two foreigners trusted with the technology of Wakanda and the armory of Tony Stark. Even when Captain America was shot dead by his enemy Crossbones, he came back to life in the story arc of Captain America: Reborn.
He has been a member of the Avengers, the Secret Avengers, the even more secret Illuminati, the Invaders, SHIELD, and even more. Steve Rogers has been in almost all of the most important teams in the world and has even led most of them.
Let's also not forget that Steve Rogers aka Captain America has been in more Marvel multimedia then my own grandma's age. He has had five solo live actions films and even more including the third film coming up and the Avengers 1 & 2. Captain America has also starred in many animated movies including Ultimate Avengers 1&2, Next Avengers: Heroes of Tomorrow, and the newest one Iron Man and Captain America: Heroes United. He has appeared in over 20 video games and has started in many more television shows. Currently he is one of the main characters in the TV show Avengers Assemble. Last but not least, he also has many action figures and toys made after him and has had a total of four novels written about him. Let's see Jean Grey top that.
Cap has also been in the front lines in every major Marvel event and has shaped the Marvel Universe in many ways. In the Secret Wars story line featured in Latveria, Captain America was part of a secret group including members such as Luke Cage and Spider-man who try to overthrow Latveria. In the Civil War story arc, Captain America was the leader of a group of rebels but is later shot dead after being arrested. In the Avengers vs X-men story arc, Captain America led the Avengers to battle the psychotic Phoenix Five, however they were not strong enough to stop Cyclops from killing Professor Xavier. In the Infinity story arc, Captain America led the Avengers to battle the builders in space. Even in the recent event AXIS the brand new Captain America is one of the main characters.
Cap is also a very interesting character as he doesn't always listen to rules. For example, he fought against Iron Man and led a group of rebels in the Civil War story arc. People think of him as a boy scout for the US. But in the 70's he lost faith in America and donned a new costume calling himself Nomad. He kept the new Agent Venom's identity a secret to the Superior Spider Man. He went against SHIELD for crying out loud. Let's also not forget the badass friends he has. He's had team ups with the murderous Punisher, friendly neighbourhood Spider-man, met Thor's father, and he's best buddies with the first black superhero in comics the Falcon.
His rogues gallery include Red Skull (he stole the mind of Professor X and Cap stopped him), Baron Zemo, crossbones, Arnim Zola, MODOK, Grimm Reaper, Von Strucker, and many more. He has also fought against the devoured of worlds Galactus (an immortal celestial), the mad titan Thanos (father of Gamora), Kang the conqueror, Ultron, and Onslaught. That's a pretty big list of A grade super-villains.
Captain America is definitely the best superhero ever because he is not only the greatest tactician on the planet but he has been everywhere and seen everything there is to know.