Many say the first computer is the "difference engine." The first of these devices was conceived in 1786 by J.H. Müller. It was never built.
Difference engines were forgotten and then rediscovered in 1822 by Englishman Charles Babbage..who is known as "the father of the Computer". This machine used the decimal numbers system and was powered by cranking a handle. The British government first financed the project but then later cut off support. Babbage went on to design his much more general analytical engine but later returned and produced an improved design (his "Difference Engine No. 2") between 1834 and 1869.
Others point out that this is the first ELECTRONIC computer. The earliest computer known is the Antikythera Machine, a mechanical device that computed the positions of the astrological signs on any given date, past or future. It was discovered in an ancient shipwreck in the Mediterranean Sea and dates to approximately 250 BC. The designer/builder is not known, but because of its similarity to other mechanical devices known to have been designed by Archimedes, it is probably his work.
Still others will say the abacus is the first computer. They were invented by the Chinese between 2600 BC and 300 BC is considered as the first computer ever. Abacus was used by the merchants and Clerks in China.
Here is still more input:
If you mean Electronic Computer, it was a man called Alan Turing from Cambridge UK, who was drafted in to Bletchley park secret base where they worked at cracking the WWII enigma codes that the Germans used every day. The Germans changed their Enigma machines to a four digit code maker. However, Because what went on at Bletchley Park the computer made from thousands of valves was kept top secret up until recently. The computer, named Colossus was smashed to pieces at the end of the war. The buildings have now been restored as a tourist center.
The Collosus Mark I 1943, the world's first programmable, digital, electronic, computing devices... its follow up the Mark II was used by British codebreakers to read encrypted German Enigma codes during World War II (notably D Day)
The first computer, or "modern computer" was invented in World War II by a German engineer, Konrad Zuse in 1941 called the Z3. More Info: "I can add some authenticity to this answer. My grandfather was a rocket scientist on Werner Von Braun's team during WWII. He was the technician who actually built the computer described above. It was an analog computer designed to simulate the guidance system for the rockets. It was built in secret because the higher-ups had not given their permission for this project."
After doing some research to answer a question for a scholarship I was applying for I found that Babbage failed to build a complete machine. The most widely accepted reason for this failure is that Victorian mechanical engineering were not sufficiently developed to produce parts with sufficient precision.
It was Konrad Zuse. He invented the z1, z2, z3, z4 and other ones. The z3 was the first fully functional program-controlled electromechanical digital computer in the world-completed in 1941. Charles Babbage just made a mechanical computing machine.
"Who invented the computer?" is not a question with a simple answer. The real answer is that many inventors contributed to the history of computers and that a computer is a complex piece of machinery made up of many parts, each of which can be considered a separate invention.
The first electronic computer was invented by Bulgarian John Vincent Ansoff. He named it the Anatasoff Berry Computer, or the ABC. It was the world's first electronic digital computer and built between 1937-42 by John Vincent Atanasoff and Clifford Berry at Iowa State University. It used regenerative memory, parallel processing, binary arithmetic and split computing functions (routines) away from memory use and management.


Now, if we're talking technical knowledge and actual precursors to the PC - IBM may have accidentally spread it around when they allowed cloning of the PC architecture. But they were not the first. [This answer refers to desktop "personal" computers. These were far from the first computers.]
These are all pre-IBM machines: MITS ALTAIR 8800, Apple II, TRS80, Atari 800 and the Commodore 64. [This answer refers to desktop "personal" computers. These were far from the first computers.]
Purists who claim that the ALTAIR was not the first, will say it was 'Simon' by Berkley Enterprises, 1950, costing $300. [This answer refers to desktop "personal" computers. These were far from the first computers.]
The first completely electronic computer was developed in England in 1943. It was known as Colossus. It took up 1,000 Sq. ft. weighed 30 tons/60,000 pounds. And took 150 kilowatts which is enough power to light up a small town.
The first computer was developed by Charles Babbage. It was called the Differential and Analytical Engine. The programmer for this computer was Ada Lovelace (first programmer). [Not quite correct. Babbage's Differential Engine was not the same as his Analytical Engine. The Differential Engine came first and was more limited.]
The first working computer (in the modern sense) was invented by Konrad Zuse. But others had created machines or ideas close to it before. These were people like Pascal, Leibnitz and Turing.

The first patent for a working computer (outside the military) was the ENIAC, created by Drs. John Mauchly and Presper Eckert at the University of Pennsylvania in 1952. They formed the Eckert-Mauchly Computer Corporation, which was later bought by Remington Rand. Their computer was used in the 1950 census and by Walter Cronkite in the 1952 Presidential election.

The ENIAC patent was declared invalid on October 19, 1973, by US Federal Judge Earl R. Larson. He attributed Atanasoff and Berry with the invention of the electronic digital computer. For more information see the related Link.

Charles Babbage invented the concept of a programmable computer in about 1856.

It partly depends on what you mean by "computer", but the earliest claim is that Charles Babbage invented the first programmable computer in 1822. The machine was called a "difference engine" and it was intended to generate mathematical tables. This machine contained 25,000 parts and weighed 15 tons. Babbage followed this with a "difference engine 2" which, although well funded, was never completed. Babbage also designed a printer to go along with the computer, but this also was never completed. In 1989-1991, the London science museum made a difference engine 2 and printer from Babbage's design. Both worked perfectly.
Konrad zuse

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