-CPT America was not an original member of the Avengers.  He was found in #4 of the Avengers comics

-Neither was Nick Fury, Black Widow, Thor or Hawkeye.

-Nick Fury knew Steve Rogers in WWII as he was the leader of the Howling Commandoes and took a variation of the Super Soldier Serum that gave him long life.

-Nick Fury was originally conceived as a white man and still is in all variations of Avengers comics except Ultimate Avengers where his likeness is that of Samuel L Jackson.

-Loki was the reason the Avengers formed together. He possessed the Hulk in attacking Thor and the city and the Avengers came to stop the Hulk with Thor in tow.

-Ant Man (founding member)  promoted the idea that the team worked well together and should form the Avengers.

-Stan Lee and Jack Kirby created the original Avengers characters in 1963.