Thunderer is a golden-age hero who also goes by the names Dark Avenger of Black Avenger. He’s Jerry Carstairs, a normal citizen who decided to become a superhero to fight Nazis!
This is the design I used as reference. In other comics or images, he has a blue hood or the colors in the image above are inverted.
I think he’s also more popular as Black Avenger; I’ll probably do a Figbash of that variant too in the future.