Which device is considered the first computer is somewhat debatable. Some consider the abacus to be the first computer. The first programmable machine was invented by Al-Jazari, but it didn't perform calculations. (It was a humanoid robot that played music.)
The first general use computer was designed by Charles Babbage, but was never entirely built, and would have been entirely mechanical. (He couldn't get the funding. Whether it would have worked with the technology available at the time is debated.) If it had been built and worked, it would have been the first Turing-complete computer (except that a truly Turing-complete computer would need infinite memory). To be Turing-complete means to be able to simulate any other computer. (It doesn't have to simulate it in real time.) In other words, it can (in theory) be programmed for any (computational) task.
The Z3 was designed by Konrad Zuse. It was the first Turing-complete computer (except for memory limitations), but was mechanical rather than electronic. It's existence was kept secret until after WWII.
The first fully-electronic computer was the Colossus. It was designed primarily by Tommy Flowers, with assistance from others at Bletchley Park. Its was also secret until after the war. (It was used to crack the German Enigma cipher (code) machine.) It was programmable only by rewiring it, and was not Turing-complete.
I think the ENIAC, designed by John Mauchly and J. Presper Eckert, was the first computer to be both Turing-complete and fully electronic, but I'm not sure. It was considered the first programmable computer until information on the computers secretly made during WWII were made public.
The first computer with a graphical display and mouse was the Alto. It was created by a small team at Xerox, but was never sold. Some consider it to be the first personal computer.
The first computer to use an x86 processor was the IBM PC 5150.
It was designed by a team of engineers led by Don Estridge.
Charles Babbage designed what was called the "Analytical Engine" which was the first stored-program mechanical computer in 1837. However his design was never completed.
In 1939, John V. Atanasoff and Clifford Berry developed the
Atanasoff-Berry Computer at Iowa State University, which was
regarded as the first electronic digital computer.
The first computer to have the components necessary to be considered a computer was made by Konrad Zuse in 1936, it was called the Z1, with its successors being the Z2, Z3, and Z4 respectively. While many think the first computer was the ENIAC, the ENIAC was only the first electronic computer, with the Z1 being mostly mechanical but with a drive motor to facilitate somewhat autonomous calculation. It was different from being simply a comprehensive calculation machine in that it could operate from a program and execute commands autonomously vs just react to given instructions.