<human>:  Who invented the first cipher?
<bot>: The first cipher was the Caesar cipher, which was invented by Julius Caesar in the first century AD. The Caesar cipher is a simple substitution cipher, where each letter is replaced by the letter that is one position to the right of it in the alphabet. For example, if the letter "a" is the first letter of the message, then the letter "b" is the second letter, and so on.