Here's a pretty good account of how MAD magazine came to be. It doesn't make the mistake that most histories do of claiming that MAD changed from a comic book to a magazine in order to avoid the Comics Code. The timing would make you think it did but actually, MAD went to magazine format to appease Harvey Kurtzman, its first editor, who was embarrassed to be in the comic book industry then.
He wanted to work in slick magazines so Bill Gaines, who was the publisher of MAD, offered to turn it into a slick magazine so Kurtzman wouldn't leave…and Kurtzman didn't leave. Not until a few months later when he was offered a classier job by Hugh Hefner. Gaines felt betrayed but he kept MAD going under a new regime and before long, he was very, very wealthy…