>>527324058
The literal first ever would be 1999 OCG Exodia where you'd Solitaire into an FTK.
The first in a real format would probably be Magical Scientist or one of the similar abusable FTKs.
The first that has people who will defend it would probably be some Future Fusion deck, either Machines or Dragons.
The first time people realized it would be a problem is likely Frogs.