The comic book that was originally launched in the 1980s as Zen Intergalactic Ninja, and is now known simply as Zen, returns to the world of comics as a monthly color book debuting with issue #0 in April.  This alien hero of the 1980s, who sold millions of comics and spawned action figures from Just Toys and video games from Konami, is returning just in time to grab a piece of the retro trend that has seen other 80s properties such as Transformers and Battle of the Planets prosper in this new century.  Co-creator Steve Stern is writing the new Zen comic series, which will be illustrated by veteran Zen artist Bill Maus.  Zen's return will be trumpeted in a full-page ad in Wizard -- and retailers will get to check out the new series in a free 16-page preview comic that Diamond is shipping to dealers this week.  Surge Licensing, the company that shepherded the Teenage Mutant Ninja Turtles from black-and-white comic book obscurity to animated celebrity, controls the exclusive worldwide license for Zen.