Nobody knows who built the first computer. This is because the word "computer" used to mean a person who did math as their job (a human computer). Because of this, some people say that humans were the first computers. Human computers got bored doing the same math over and over again, and made tools (mostly mechanical calculating devices like abacuses) to help them get the answers to their problems. Over time these machines became computers.
[change] Automation
Humans have a problem with math. To show this, try doing five hundred eighty-four times three thousand two hundred twenty in your head. It is hard to remember all the steps! People made tools to help them remember where they were in a math problem. The other problem people have is that they have to do the same problem over and over and over again. A cashier used to make change every day in her head or with a piece of paper. That took a lot of time and people made mistakes. So people made machines that did those same things over and over. This part of computer history is called the "history of automated calculation," which is a fancy phrase for "the history of machines that make it easy for me to do this same math problem over and over without making mistakes."
The abacus, the slide rule, the astrolabe and the Antikythera mechanism (which dates from about 150-100 BC) are examples of automated calculation machines.
