A lot of people don't know this, but the original Unix was called nix. But rather than the 1.0, 2.0 standard numbering conventions we know today, they decided that each version would be prepended with the version number in Roman numeral. So it was
Inix
IInix
IIInix
IVnix

When they were going to release the 5th release, an intern didn't understand the naming convention, misread V as U, nobody in Q/A realized the typo, so it accidentally released as Unix.

Everyone kinda liked the idea of poking fun at the intern's mistake, so they just stopped incrementing the name after that and left it called Unix for the mainline release.

Others still kept releasing their own forks and reimplementation of Unix after, so we had IXnix and XVIIInix. There was much laughter about XXXnix, but it never gained much adoption outside of a very specific userbase. Someone decided to make nix 101 as a reference to an intro level course number in US universities, so it got the name MInix. The next popular release was nix 51, so LInix.

This one wasn't created and blessed by the owners of the nix trademark, and they didn't like this upstart beginning to take some users from Unix (it has become corporate owned by that point, not a Bell Labs hobby project). A long nasty spat went back and forth for a while, before just to settle the case, LInix renamed itself the Linux we know today.