We live in a time where you can watch the most explicit hardcore pornography on the same phone you use to call your mother. But it wasn’t always that way.

The adult industry didn’t exist on any kind of serious scale before Hugh Hefner and Bob Guccione came along. By their heyday in the 1970s, Playboy and Penthouse each had upwards of five million readers, and that’s not counting how many times a single copy was passed around.

This six-part series follows as magazines once chastely stowed under merchant counters gain over-the-counter acceptability. And as both men fight for market share, the question is: how far will they go to grow their erotic empires?