The Commodore 64 is an American microcomputer that was released in 1982. This computer would become one of the more widely used 8-bit computers of the era, and likely defined more than just a generation of gamers. The computer didn't stop being sold until the 1990's, and even now still has a very lively userbase (with some of those users being emulator users, like me). The system was named for its 64 kilobytes of memory (which was a lot back then).
While most people born in the 2000s and later may not have heard of it, it's pretty much unavoidable if you ever look into the various ports of arcade games and other titles. Computers like the Commodore and ZX Spectrum raised a generation of computer programmers, and I would argue that in some ways they had it easier than us...
The C64 could display 16 colours at once, but it was limited as to how you could. Standard graphics modes could be considered high-res mode, while modes that show more tended to have to take a bit away from the resolution in order to achieve what was asked. According to the C64 Wiki, there were only five officially supported graphics modes (though homebrewers and hackers are insane, so there are multiple other techniques people used over the years).
The unique sound of the Commodore 64 is thanks to its sound chip, often just called the SID. There were multiple programs used to write music for the system, but some people would also write music in assembler (and apparently BASIC is capable in some ways, too).
Thanks to the Commodore 64 running a flavour of BASIC, pretty much anyone who wanted to could make a game. There are multiple magazines for a variety of microcomputing systems that would often publish programs made by other people, for readers to copy down and try at home. Learning BASIC through these magazines (and with the help of books that may have come with the computer) was fairly easy, since you're bound to wind up debugging someone else's code.
Many companies from Atari to Nintendo (through other companies) made ports of their games for the Commodore 64. Aside its plethora of ports, many companies also made games that were to release on the Commodore first, and there were lots of games that would be ported from one microcomputer to the next. One example of this is International Karate, which originally was a ZX Spectrum game before its sequel was ported to both the Commodore 64 and Amstrad CPC.
The computer also still has a very lively homebrew scene, with developers like Arlasoft making multiple ports and other projects for the system. In 2020, a version of Fix-It Felix, Jr. from the movie Wreck-It Ralph was released for the C64. There's also a procedurally generated version of Ms. Pac-Man for the system called Lady Pac. You can generally find multiple games on sites like CSDb, including multiple cracks of the same game by different groups.