The Avengers made its debut in The Avengers #1 (Sept. 1963), created by writer-editor Stan Lee and artist/co-plotter Jack Kirby, inspired by the success of DC Comics' Justice League of America.
The original team was first led by Iron Man (Tony Stark), with its pioneer membership in Thor (Thor Odinson), Hulk (Bruce Banner), Hank Pym (Giant Man/ Ant-Man/ Goliath/ Yellow Jacket), and the Wasp (Janet van Dyne).
After its debut, and in the decades that followed, we saw some new additions and departures of heroes with powers or not.
Even when you are a follower of the team, you'd be surprised at how some were once a member of this prestigious team of protectors. Some very briefly, some affiliated, some sacrificed their lives for the glory.
We shall list the new recruits out according to the decades that followed:
Captain America, Haweye, Quicksilver, Scarlet Witch, Swordsman, Hercules, Black Panther, Vision, Black Knight.
Black Widow, Mantis, Beast (X-Men), Moondragon, Hellcat, Falcon, Ms Marvel, and the time-travelling Two-Gun Kid.
Wonder Man, She-Hulk, Tigra, Captain Marvel, Namor, Starfox, Dr Druid, Mockingbird, Thing, War Machine, Moon Knight, Firebird, Demolition Man (not Stallone), Mister Fantastic, Invisible Woman, Human Torch, U.S. Agent, and Quasar.
Spiderman, Sandman, Rage, Sersi, Stingray, Spider Woman, Machine Man, Living Lightning, Crystal, Darkhawk, Thunderstrike, Justice, and the sexy Firestar.
Shortly after the millennium, the storyline branched out to several titles with massive twist and turns to woo more readers.
And so we shall end the list before the spark of the first Civil War, otherwise this shebangs could go on forever...
In the year 2000:
3-D Man and Silverclaw joined the team. The former was also known as Triathlon.
When it's 2001:
Jack of Hearts joined the team, but he was killed 3 years later.
We see Scott Lang finally gaining full membership as Ant-Man, but with a twisted fate thereafter...
Lionheart joins the team. She was formerly known as Captain Britain. Why female? Long story....let Google tells you....
Subsequent years were hectic and erratic, when we saw many shortlived additions, with bulk of them being killed off eventually:
Wolverine - 2005
Luke Cage - 2005, departed eventually
Sentry - 2005, killed later
Ronin - 2005, killed later. FKA Echo.
Ares - 2007, killed later
Amadeus Cho - 2009
Jocasta - 2009, departed and rejoined as a substitute
Stature - 2009, killed later
Vision - 2009, the Jonas "variant", killed later
Post Civil War
After 2009, the storyline took a massive and wild reboot when things get incredibly complicated. So much so you could see almost the entire team of the "X" family joining the Avengers, and of course almost anybody from the Marvel Universe you could name would probably have a membership with them, making your membership with the furniture maker IKEA looks so prestigious and exclusive.
And if you have any interest in knowing, it wouldn't be too difficult to dig up from the internet, but may take a while to digest.