Who developed the world's first microprocessor?
A microprocessor is generally defined to be a single-chip central processing unit (CPU). To earn the name, a microprocessor does not have to include the program memory (e.g. ROM) data memory (RAM), or peripheral interfaces (e.g. serial ports), but many modern microprocessors include all of these.
The Intel 4004 is widely considered to be the world's first microprocessor. Wary of spurious lawsuits, Intel makes no such bold claims, but there is no doubt that the 4004 was the first customer-programmable microprocessor to reach the commercial market. You simply could not buy anything like it before its introduction on November 15, 1971.
To be fair, during the 1970-1971 period of Intel's 4004 development, Texas Instruments (TI) was also working on 4-bit CPU-on-a-chip technology for use in their line of calculator products. Regardless of who might have achieved "first silicon," there was a key difference between Intel's and TI's efforts. Although TI was developing a chip that contained all the elements of a microprocessor, it was designed to perform only one purpose, to be the "brain" of a calculator. Intel was also developing the 4004 for calculator applications, but their CPU-on-a-chip architecture could be programmed to control a wide variety of electronic devices from traffic signals to test equipment, according to the instructions stored in the external ROM. After the 4004's debut, Intel actively developed the nascent microprocessor market with their line of design tools like the Intellec 4, whereas TI focused on the "calculator on a chip" market for five years before finally releasing their TMS1000 family of 4-bit "microcontrollers" in 1976, which integrated the CPU, program ROM, data RAM, and I/O logic into a single chip. By then Intel had already introduced their famous 8-bit 8080, but there was plenty of market opportunities for TI's far less expensive, 4-bit "computer on a chip." Not long after, Intel introduced their own microcontroller family, the most famous being the 8-bit 8051, possible the most "cloned" microcontroller of all time and still in active use today.
Like the surprise witness who appears at the end of television courtroom dramas like Perry Mason or Law and Order, in 1998 the U.S. Navy declassified details of the F-14 "Tomcat" jet fighter avionics. This introduced new questions about who were the "real fathers of the microprocessor." Developed by Garrett AiResearch in the late-'60s and deployed a year before the 4004, the Central Air Data Computer (CADC) is responsible for directing the F-14's flight control surfaces and displaying pilot information. With its pipelined, 20-bit datapath, the CADC is architecturally more advanced than the 4004 in many ways, but after some debade, it was eventually agreed that the CADC isn't a microprocessor in the generally-accepted sense of the word. Beyond the fact that its microsequencer and arithmetic units are partitioned into several chips, the CADC has no flow-of-control instructions (jump, conditional branch, call etc.). The program continually loops, and processor uses "data steering" instead control flow to make decisions. This approach has the advantage that the datapath's pipeline always stays full. Though out of the running as the first microprocessor, one could argue that it was the world's first LSI digital signal processor (DSP).