I’ve always heard them called Bessler stairs, so I’m assuming that they were invented by the Bessler Stairway Co., still in business. I’m just having a hard time finding good confirmation of that on the web.
And I recall two different styles: one with a single piece ladder section that pivoted down on rails, while the other had a two-piece ladder section that unfolded after being lowered.
I sat on a focus group that was tasked with discussing injuries involved with these kinds of stairs. Obviously, I Indicated that the stair company was guilty at every step.
I had fun just scrolling and scrolling thru that looking at the ads. Came across one other ad for drop-down stairs: also Bessler. Didn’t come across any other companies selling them after looking thru quite a lot of pages. Given the multiple ads for all sorts of things, this might be telling.