Began with Eldritch Wizardry in 1975/76, so, pretty much, it's been part of D&D since the earliest days.
Good to know- I have those books, but never played under that ruleset. I was introduced to D&D in '78 with the 1Ed AD&D PHB...and no, our DM wouldn't allow us to look at the other 2 books.
Ahhh...good times, good times.