I remember when I realized I had been using Microsoft all along through my Commodore 64.

The Commodore 64 got me started in computers, back when I was in grade school. Countless late nights programming in BASIC. All this time I never knew BASIC was licensed from Microsoft. Thanks!

"Commodore licensed BASIC from Microsoft in 1977 on a 'pay once, no royalties' basis after Jack Tramiel turned down Bill Gates' offer of a $3 per unit fee, stating, 'I'm already married,' and would pay no more than $25,000 for a perpetual license."

https://en.wikipedia.org/wiki/Commodore_BASIC