Though they are the Marvel Universe's most front-facing superhero team, the Avengers have plenty of secrets. In the past, the team has hidden things like alien races, supervillain plans, and even world-ending plots from mad gods. However, some of the biggest secrets come from individual members, rather than teams.
Some heroes with Avengers memberships keep things secret to protect themselves and their loved ones, while others do it for a greater good. Some Avengers house secrets for reasons of nationalism or personal profit. Regardless of motive, many of Earth's Mightiest Heroes keep things close to their chests.
10 Thor
As one of the most powerful Avengers, it may be strange to think of Thor as needing to hide anything. Regardless, Marvel's God of Thunder has plenty of secrets. As king of Asgard, Thor's duty is to protect Asgard's state secrets and its citizens from threats like the Dark Elves and Frost Giants. Most notably, however, is Thor's secret identity.
For a time, Thor masqueraded as construction worker Sigurd Jarlson. Prior to and after that, Thor had a human alter ego named Don Blake. Though initially created as a disguise for Thor by Odin, Thor grew into his Blake persona and tried hard to mask his dual identity from Jane Foster and Tony Stark.
9 Iron Man
Tony Stark declared that he is Iron Man in a key character moment, but the Armored Avenger kept his identity secret for years. Stark felt keeping his identity as Iron Man hidden was critical for a variety of reasons ranging from his personal safety to the welfare of his company.
While Stark's identity being public eventually became a crucial part of the character, Stark has remained secretive. Though it often doesn't work out, Iron Man has continually tried to keep his weapons and armor technology secret. Stark has also made a habit of secret backroom deals with certain fellow heroes, particularly those in the Illuminati.
8 Gilgamesh
Not all Avengers are secretive by choice. In the case of Gilgamesh, the hero was the subject of many of humanity's greatest myths. However, due to his tendency to move and the passage of time, Gilgamesh gained the epithet of "the Forgotten One."
Even as a member of the Avengers, Gilgamesh was sometimes met with confusion as to who he was. Gilgamesh also spent some time in exile from his fellow Eternals, something that further added to his mystique. Ironically, Gilgamesh entered exile because of his tendency to meddle in the affairs of humans, something that if he had kept doing would likely have made him appear less secretive.
7 Sersi
Another Eternal, Sersi has been far more intentional in her attempts at secrecy than Gilgamesh. However, Sersi maintained her secrecy in a counterintuitive manner. Rather than hide away, Sersi used her assumed identity to become a New York socialite, reveling in the fame that her wealth and penchant for parties brought.
Of course, Sersi has always kept her true identity hidden. She teamed with Thor in the 1100s, but the Norse God was not aware of their having met until much later. As Sersi spent more time in the modern Marvel Universe, she has retreated more from the public eye and to the bastion of the Eternals.
6 Black Panther
Black Panther is often the king of Wakanda, but the nation's very existence was kept hidden for years. Even when it was revealed, T'Challa took his role as protector of the country very seriously. Even in present continuity, the secrets of Wakanda remain successfully shrouded.
Other aspects of T'Challa's life are as secretive. T'Challa and his allies also hide the Heart-Shaped Herb that gives him his powers so others may not access it to cause havoc. T'Challa also keeps some of his activities as king secret from his fellow Avengers as to mitigate conflict.
5 Spider-Man
Out of all the Avengers, few try harder than Spider-Man to keep a secret identity. Ever since his brash actions caused Uncle Ben to die, Spider-Man has protected his identity with the utmost importance. Spider-Man's full facemask is the most obvious evidence of this, but there have been several other notable instances of Spidey's secret-keeping.
The most notorious instance of Spider-man's need for a secret identity was in the events of "One More Day," when Peter Parker sold the existence of his marriage to Mephisto as part of a bargain that restored his secret identity. Another instance was when the U.S. government denied Spidey entrance to the Avengers precisely because he wouldn't reveal his identity.
4 Ares
As the Greek god of war, Ares has been a highly visible figure for thousands of years. Ares makes little effort to conceal his identity, as evidenced by his use of his first name as his nom de guerre. However, there is one major thing Ares tried to keep secret.
When he was a member of the Mighty and Dark Avengers, Ares desperately sought to keep the existence of his son Alex a secret. This was largely because Alex was an incarnation of Phobos, the Greek god of fear and Ares did not want him to be exploited by others in search of powerful superhumans.
3 Black Widow
As a former spy for the Red Room, Natasha Romanova knows how to keep a secret. Even in her more heroic career, Black Widow has continued to keep secrets: for S.H.I.E.LD., for the U.S. government, and for the Avengers, not to mention herself.
The Widow's ability to keep secrets has proven invaluable, such as when she was assigned by Iron Man to transport the shield of the deceased Steve Rogers. However, her conditioning by her former Soviet controllers gave her many false memories. Because of this, even when Black Widow thinks she is telling the truth, her brainwashing might be hiding further secrets.
2 Winter Soldier
Like Natasha Romanova, Bucky Barnes has undergone years of brain-altering treatment by the Soviet Red Room. However, Barnes's transition from acting as an operative of that group was much more difficult. Captain America forced Bucky out of his brainwashing using the Cosmic Cube, an event that restored his memories but deeply traumatized him.
Barnes was overwhelmed by guilt because of his past actions. Because of the violent nature of many of his memories, Barnes has buried them even from people he trusts. Though Barnes has attempted to work through his difficult past, the hero still has trouble sharing every element of it.
1 Namor
Marvel's Prince of Atlantis is many things: arrogant, brash, regal. These traits often overshadow his secretive nature. The Sub-Mariner's need for secrets is similar to Thor's and Black Panther's. As the ruler of a nation, it is crucial for him to protect its secrets, often from those he is fighting alongside.
A member of both the Illuminati and the Cabal, Namor has kept huge secrets from many of Marvel's most prominent characters. Ranging from the location of his people to the truth behind incursions, Namor has continually proven himself one of the Avengers' most secretive members.