By 1974, MAD magazine had hit an all-time high in popularity, selling more than 2 million copies per issue. It was also the height of the Watergate scandal, Vietnam War protests, and the counterculture. MAD helped bring about the age of subversive satire that we see today everywhere from “The Simpsons” to “The Daily Show.” It was the underground before there was an underground. And, among the wackiest of cartoonists, in fact, “MAD’s Maddest Artist,” was Don Martin. Martin was from some other planet. “MAD’s Greatest Artists: Don Martin: Three Decades of His Greatest Works,” published by Running Press, lets you see this extraterrestrial cartoonist at his best.