In English, when we give an example and it has to contain a person, there are some default names that we resort to, such as John Doe, John Appleseed, or Alice & Bob. I even found this line on wikipedia about John Doe:
John Doe (male) and Jane Doe (female) are multiple-use placeholder names that are used when the true name of a person is unknown or is being intentionally concealed.
In Chinese, there are similar names 張三 and 李四 that we use for the same purpose. I'd like to know if there are any such placeholder names in Japanese?