Great defense and great nicknames—two things that gave the NFL personality and reputation in the 1960s and ’70s. Names such as Deacon Jones, Bob Lilly, “Mean” Joe Greene and Alan Page were synonymous with toughness. When running backs still ruled and the passing game was still evolving, stifling defenses dished out some of the roughest punishment football has ever seen. We look at some of the best defensive units in history, along with the colorful nicknames that made them fan favorites. Purple People Eaters The Minnesota Vikings in the late-1960s through the ’70s made it to the post season 10…