On September 29, 2011, Gavin Andresen made the first pull request aimed at adding the functionality of signing a transaction with multiple keys.
Later, his proposal was edited, but it became the first version close to what we today call "multisig".
Multisig is a scheme for storing and spending coins designed to enhance the security of interacting with Bitcoin and introduced the possibility of joint coin custody.
Find more info on multisig below 👇