Illegal content of block 229k Updated +Created
These can be viewed at bitcoinstrings.com/blk00052.txt and are mostly commented on the "Wikileaks cablegate data" section of Hidden surprises in the Bitcoin blockchain by Ken Shirriff (2014).
Soon after block 229991 uploaded the Satoshi uploader, several interesting files were added to the blockchain using the uploader, and notably some containing content that might be illegal in certain countries, as a test to see if this type of content would make the Bitcoin blockchain illegal or not:
So basically, this was the first obviously illegal block attempt.
None of this content is particularly eye-popping for Ciro Santilli's slightly crazy freedom of speech standards, and as of 2021, the Bitcoin blockchain likely hasn't become illegal anywhere yet due to freedom of speech concerns.
Furthermore, it is likely much easier to find much worse illegal content by browsing any uncensored Onion service search engine for 2 minutes.
Ciro Santilli estimates that perhaps the uploader didn't upload child pornography, which is basically the apex of illegality of this era, because they were afraid that their identities would one day be found.
Bibliography:
Evil Updated +Created
Things that are not nice such as: