The question does not have a simple and straightforward answer.
Charles Babbage invented, but did not build, an ‘Anylitical Engine’ which was mechanical programmable computer in the 19th century. Subsequently it has been proved to be workable.
An abacus is a kind of computer which predates most of western history.
The decoding specialist at Bletchley Park created an electronic computer (Called variously a ‘bomb’ or ‘bombs’ which was also programable. perhaps mainly through the genius of Alan Turing.
Commercially, perhaps ENIAC is recognised as the first electronic computer.