Memes

Worse: X AE A-XII Musk (only named this because X Æ A-12 was not acceptable to California regulations due to having non-English characters both in the form of numbers and of Æ), and later, another named Exa Dark Sideræl Musk (nicknamed "Y"). Both of these were with Grimes. Both of these are the official names given to these children, that is what is written on their birth certificates.

However, they were also preceded by around 8 other children with different women given much more normal names, so it's unclear how much influence Grimes had on the decision making here. X AE A-XII in particular though I will definitely attribute to Elon because his fixation on the letter X extends back decades at this point.