[mikorym]

> A monad is a concept that belongs to a branch of mathematics called category theory, where it was introduced in the 1960s.

No. [1]

[1] General Theory of Natural Equivalences, Mac Lane and Eilenberg, 1945.

https://www.ams.org/journals/tran/1945-058-00/S0002-9947-194...

[mikorym]

Sorry, I misread; monads were only introduced later. The above paper introduced the field of category theory itself.