But then the turtles’ cartoon series launched during the 1987 holiday season. A now-classic live-action movie followed in 1990. There were popular video games and tons of toys and merchandising. The turtles had outgrown their comic book origins. “The Last Ronin” became lost in the wave of “turtle power.” Eastman, in a recent interview, estimates that for most of the 1980s, he and Laird spent 90 percent of their time on TMNT comics and the other 10 percent on business. Once Hollywood called, he says, those numbers were switched...