Anyone who's been reading comic books and/or watching comic book movies for any length of time knows that superhero origins are subject to change. This has been going on since the Golden Age. We discussed some early Blue Beetle origin revisions recently, and a similar situation developed with another Fox Features Syndicate hero named Green Mask. Both characters had debuted in Mystery Men Comics #1 in 1939 and were rebooted with added superpowers when they both received their own series early the next year. In Green Mask's case, he was bombarded by power from a "Vita-Ray machine", giving him incredible strength and other abilities plus a sidekick as well — and this would not be his last reboot during the Golden Age. Several issues of the series have covers that are coming to greater collector attention in recent years, and issues like #6 and #8 along with many other issues of the series up for auction in the 2022 December 1 Fox Comics Showcase Auction #40214 at Heritage Auctions.
Most of the major Fox Feature Syndicate superheroes have a sort of organic evolution of their abilities and backstories over time, and the Green Mask is probably the most pronounced example of this from the Fox lineup. In fact, the character has two points in its history that would qualify as reboots by today's standards. While there appears to be some difference in opinion as to whether the character who debuted in Mystery Men Comics #1 is the same person as the character who debuts the next year in Green Mask #1, I think they are best understood as having different and unrelated secret identities. The version of Mystery Men Comics #1-12 is a pulp-style mystery man with no special abilities beyond basic athleticism and fighting skill and used no special weaponry or gadgets beyond a normal handgun. The introductory blurb in the first issue alludes to the character as having a secret identity, but it is never named, and he is never shown in any form besides the Green Mask. In fact, the only other regular character of the feature, newspaper reporter "News" Blake, typically does much of the leg work in these stories, leaving Green Mask to round up the bad guys in the end.
The debut of the character's own series in Green Mask #1 significantly changes this equation. The character is now identified as Michael Shelby, son of a United States Senator. The Senator is assassinated by members of a villainous secret society called the Grim Circle. The attack leaves Michael Shelby near death himself, and in an attempt to save his life, his friend Professor Lascomb uses his "Vita-Ray Machine" on Michael's mortally wounded body. The procedure works even better than expected, giving Shelby the power of flight and general superhuman strength. He decides to become the Green Mask to avenge the murder of his father. In the same story, the sidekick Domino the Miracle Boy is introduced, after a young boy is injured in an attack on the Green Mask and the Vita-Ray Machine is used to save him. This version of the character, which appears in Mystery Men Comics #12-31 and Green Mask #1-9, was effectively ended by Victor Fox's Fox Publications, Inc. 1942 bankruptcy.
When Fox emerged from his financial strife in 1944 and started to put a comic book line back together again, Green Mask returned in Green Mask #10 as a completely different character. He is now named as a man named Walter Green, whose son Johnny Green also has the power to become the Green Mask. But Walter Green is never shown in the series. Instead, Johnny Green, who is depicted as a young boy, transforms into the adult Green Mask when he is angered by witnessing wrongdoing. It is essentially the Billy Batson / Captain Marvel dynamic, but Johnny Green essentially falls asleep during the transformation and wakes up without memory of what has happened when the adventure is over. After one more issue of the original Green Mask series, the title was relaunched with volume 2 which lasted six issues.
The Green Mask series has ridiculously low CGC Census numbers, but issues like #6 and #8 along with many other issues of the series up for auction in the 2022 December 1 Fox Comics Showcase Auction #40214 at Heritage Auctions. If you've never bid at Heritage Auctions before, you can get further information, you can check out their FAQ on the bidding process and related matters.