Bruce Lee did dragon flags often, but they were popularized by Rocky when he was training to beat the hell out of Ivan Drago in Rocky IV. They're exceedingly tough to do, especially if you've never done them before. They're also pretty much the most impressive looking movement you can do in a gym.
Even though they're tough to master, this relatively easy progression takes you from reverse crunches to true dragon flags in no time.
When I first approached corrective and performance exercise specialist Paul Chek about writing for Testosterone, his first concern was whether I'd choose to soft-peddle his article. In other words, he was worried that I'd try to "dumb down" his material.