Bar Exam And Reqs to become a laywer?

I keep hearing cases of people becoming lawyers and taking the Bar exam, without having gone to law school. Either they attended college and got base degrees, or haven't and just studied for and scored very highly,and went onto become lawyers....i need concrete evidence of this...at one point people didnt have to go to grad school to move on in a profession...does the same still hold true nowadays.... what exactly must one do to become a laywer? what are the reqs for the bar and for recognition as a lawyer?