After thinking about my other post about Bitcoin Testnet being directly related to Satoshi.
I realized Bitcoin Testnet is actually the first Altcoin ever... previously I had it in my mind that the first was Namecoin, but technically speaking Bitcoin Testnet came first.
Here is a post from Gavin to Andreas on Twitter in 2014. (I'm slow, but better late than never)
https://x.com/gavinandresen/status/499247483286224896As an early operator in the crypto space, this takes me way back! Thanks for the trip down memory lane!

I still remember getting a bunch of Bitcoin, Litecoin and Namecoin stickers that I bought from someone here on bitcointalk, and to think now that there were only 3 cryptocurrencies back then is pretty crazy. Namecoin came before Litecoin, I think, but not by much.
Yes, I agree that the Bitcoin Testnet was the first altcoin, theoretically and chronologically. However, when it comes to use cases, I disagree, as the Bitcoin Testnet was essentially created for experimentation, as it's name.
Regardless, whether Bitcoin Testnet is the first altcoin or not isn't an important discussion, because people will have their own definition & image of the first altcoin, just like what I exemplified in the first paragraph.
Back then Namecoin had some utility, but not much traction. It was definitely the first real altcoin, and then when Litecoin came along it brought with it the parallels of Bitcoin being like gold, and Litecoin being like silver. What people really appreciated about it though was the ease of mining, and the utility of Litecoin's faster transactions. I have to say, I do miss those days a little!