Bio: Mark Mason was an investigator for the O.S.S. during the later days of World War II. He hired Louise Grant as his secretary.
Louise soon fell in love with Mark and developed the superhero identity of The Blonde Phantom so she could spend more time with him. Mark developed eyes only for The Blonde Phantom and continually ignored Louise. After many adventures together and tired of not having the man she loved know who she was, Louise told Mark she was also The Blonde Phantom. The two were married right away in 1949.
In regards to his appearances in comic books, Mark Mason basically stopped appearing altogether in early 1949. It's revealed through flashbacks in The Sensational She-Hulk #4, that Louise Grant, now Louise Mason, knew she was a comic book character and found her way into becoming a supporting character in The Sensational She-Hulk comic book. She did this because she knew that comic book characters in the Marvel universe age at a distinctly different rate when they're appearing in the books as opposed to when they're not appearing in the books. She informed She-Hulk that after seeing Captain America and Namor make comeback appearances in Marvel books, her and Mark waited for their turn, sure that they would get the chance to star in comics again. That never happened, and aging as one normally would in real time instead of comic book time, Mark died at the age of 72.