The first mined block contained a purposeful message inside the block:

"The Times 03/Jan/2009 Chancellor on brink of second bailout for banks."

It was placed there on purpose by Satoshi to show the demise of the fiat money and banking system.

And of course the need for bitcoin.

Anyone can put text into a block, their name, a short message, etc.

However, earlier this year, some bitcoin developers figured out how to put longer inscriptions(text) into a block via some 'hacks'(my term). Some made qr codes, ot bitmap images, some plain text, others fit a small game into a block, etc..

It has now been used for the war logs, Panama papers, other cables, 3d printed gun files, and on and on. Permanent and undeletable.

You need a special blockchain explorer to easily see them however.

You can go here:

https://ordinals.com/inscription/911bffcff4608ab49e639ac55c314d1d8c2b97b51b5573454a5143350f175258i0

To view the first of the inscriptions for wiki leaks.

Good luck! I hope this helps, lol.