Non-transactional data has been present on Bitcoin from the very beginning. The Genesis Block (Block 0), mined by Satoshi Nakamoto on January 3, 2009, contained the message “The Times 03/Jan/2009 Chancellor on brink of second bailout for banks” embedded in the coinbase parameter . This is the first instance of arbitrary, non-transactional data on the Bitcoin blockchain.
Every mined block has a coinbase field of up to 100 bytes that normally contains data like the block number, timestamp, and difficulty, but can include arbitrary data . Satoshi used this field to embed the Times headline, likely both as a timestamp proof and a political statement about the banking system.
People rapidly figured out how to encode arbitrary content into the Bitcoin blockchain by using hex data in place of Bitcoin addresses , and early examples included things like the Bitcoin logo image hidden among normal transactions. Later, the OP_RETURN opcode provided an official method for embedding small amounts of arbitrary data in transactions.
So in short — non-transactional data has been there since literally day one, block zero.​​​​​​​​​​​​​​​​