The Intel 4004 was invented between 1969 and 1971 by Federico Faggin, Ted Hoff, and Stanley Mazor. It was a 4-bit central processing unit released by Intel Corporation and was the first microprocessor.
The Intel 4004 was the first random logic circuit integrated in one chip and was the first processor to use the metal-oxide-silicon (MOS) process. It was first used for a Japanese calculator but later used for various technoloies such as calculators, cash registers, and ATMs.
One interesting fact about the Intel 4004 is that it was the first commercially available monolithic processor.