What is the origin of the Leadership concept in D&D?

In 3.5 D&D there is a Leadership Feat. It allows you to gain a cohort and some followers, a whole bunch of followers if your score is high enough.

But, what is the origin of this Leadership concept in D&D, where did this idea of leading a whole group of people come from, and why is this even an option given that most games seem to revolve around only the player characters rather than characters + groupies? That would be a whole lot of people to keep track of if every player character was a leader!

I would like to know about the background and history of this concept in D&D, or is it new to the 3.5 edition?