In 1984, this orange tabby housecat, real name "Fatso," was dressed up in baby clothes by her owner and videotaped "playing" the keyboard. Really her owner was moving her paws under the shirt. Just some America's Funniest Home Videos-level stuff. Fast forward to 2007, when this owner put the video on YouTube.
Annnnd it sat there unnoticed for two years, an epoch in Internet time.
But then in 2009, someone else used a clip of Fatso after a fail video with "Play him off, Keyboard Cat," and a meme was born!