This is "In The Spotlight So Clear," a feature where we spotlight times in comics where characters need to be cleared out of the way to make room for a new status quo. Like, for instance, you want to introduce a new Captain Superhero, you might want to first get rid of the previous Captain Superhero. Stuff like that.
Reader Carlos M. wrote in to ask, "I have a question, when and why did Captain Mar-Vell change his costume?"
This is a bit trickier than you would first think, because while Gil Kane designed Mar-Vell's new costume, he didn't actually draw the first appearance of said costume and so people sometimes get thrown off by not knowing that the previous issue actually explained how the costume came to be! Instead, the previous creative team on the series actually set up Thomas and Kane's iconic run!
When Mar-Vell debuted in Marvel Super-Heroes #12 (by Stan Lee, Gene Colan and Frank Giacoia), he wore the uniform of a captain in the intergalactic Kree fleet.
He was, in fact, literally just a dude named Captain Mar-Vell.
Obviously, that changed when he ended up being stuck on Earth and deciding to defend his new planet. The humans hear "Captain Mar-Vell" and they think his name is Captain Marvel and that ends up becoming his adopted superhero name.
But his superhero costume remains his Kree captain's uniform. Obviously, over time, people weren't exactly thrilled with that uniform, so when Roy Thomas and Gil Kane tried to revive the flagging sales on the series, Kane (with colorist Michelle Robinson) re-designed the Mar-Vell's costume, giving him a bold and colorful new look...
The reasoning for the new costume, though, was not revealed by Thomas and Kane, but rather by the previous creative team on the series! In fact, they were the first people to show the dramatic new look for Mar-Vell!
Captain Marvel managed to maintain a monthly release schedule after the Kree hero got his own series, but it is interesting to note that he also had a pretty wide variety of creative teams on his series before Roy Thomas and Gil Kane came on board (and even then, do note that the big Thomas/Kane revamp did not exactly set the world on fire, sales-wise, either, and the series was effectively canceled a couple of times before Jim Starlin took the series over and revamped it even further by turning it into a cosmic adventure).
Arnold Drake took over the book from Roy Thomas after Thomas launched the book. Drake wrote it from #5-12, with Don Heck drawing #5-10 and Dick Ayers #11-12. Then Gary Friedrich took over, working with Frank Springer and Tom Sutton from #13-15. With one issue to go before Thomas and Kane took over, Archie Goodwin, Don Heck and Syd Shores came on board to set up Thomas and Kane's run.