WWW II.. PT boats.. then there were a bunch of "experiments' in Europe.. then trickled to US. I saw a stepped hull from the 70's. (almost bought it) but I think the first "production" steps were in the late 80's early 90's/ Most major builders start doing it around the same time. Early 90's.
My dad had a steped wood boat in the late 60's.
Challanger Offshore Hull No. 1 in 1994 had blackhawks and Harry's step. (later the AT step)
A good question would be who has the "Best step" ???