It pains me to say I’ve used Photoshop before the days of the ‘layers’.
I remember fumbling around in it during advertising art class in high school. I thought it was the most difficult program ever. I’d rather do paste up. (You can Google that.)
Photoshop has certainly come a long way since it’s release in 1990. Here’s an interesting read about how Photoshop came to be and a history of all the versions.