What started the Ground Beef meme?

[Mr. Vulcanator]

[SniperED007]

I heard it started when a couple of cows got legless one Friday night.

[Shedding]

When a cow lost one leg and now it is lean beef.

[tourist]

"None pizza with left beef" will be ten years old in october.

That can be traced back to an old Wendy's ad in 1984:
https://www.youtube.com/watch?v=Ug75diEyiA0

The main school of thought has the meatgrinder as central to the theme and origin too. There are many examples.
https://www.youtube.com/watch?v=UcUPGAth6OY

The Humoral Theory directly influenced the preferred cooking methods for certain foods: beef was boiled because it was "dry" and "cold," while pork was roasted to dry out its "wet" humor. The theory also influenced texture: many period dishes contained well-ground, minced, chopped, or sieved ingredients because those techniques would completely "mingle" the ingredients and thus ensure the dish was easily digested.
http://www.katjaorlova.com/MedievalKitchenEquipment.htm