The Credits page on the menu is a place where it shows all the people that helped create Tower of Hell and the roles they had in doing so.
The credit for game design goes to the owner of Tower of Hell, PyxlDev, and co-owner of Tower of Hell, ObrenTune, as they were the ones who originally made the idea for the game and created it.
PyxlDev is given all the credit for the programming side of the game.
PyxlDev created the menu GUI, presumably through programming rather than an image. He is given credit for making the interface here that includes things like the Shop, Effects, and even these Credits.
LeetLego was involved with making some of the graphics for the game as well as the images for the Badges. Alongside that, PyxlDev made some of the graphics, presumably including things like effects that came before LeetLego joined the staff team.
Evanbear1 and BriefSerendipity are given credit for the music they created, all of the music currently in the game is created by one of these 2 developers.
You can see who made which of the soundtracks on the ToH Music Playlist page.