Defenders members: Namor, Dr. Strange, The Hulk
The origin of the Defenders:
the founding members gathered to battle the alien techno-wizard Yandroth, who had invented a machine that could set off nuclear stockpiles all over the planet, and remained as a team afterwards. Due to the popularity of their tryout in Marvel Feature, Marvel soon began publishing The Defenders.
Invaders members: Captain America, Namor, Human Touch "android"
The origin of the Invaders:
When these superheroes saved the life of British Prime Minister Winston Churchill from Master Man, the thankful Churchill suggested that they should become a team, known as the Invaders.