I see the user called "delete" at several places in the older questions. However, I can't view his profile or anything. I was just wondering, who is delete? Why can't I view his profile?
It's an account that has been deleted as requested by the user who was using it.
Users cannot delete their own account, but they need to change the username to "Please delete" (or something similar), add a note in the user profile, and send an email to the Stack Exchange staff. After that, they will take the necessary actions to remove the user account; the posts done with that account, when they don't have a score of −3, will be left on the site.
The purpose of adding a note in the user profile is to give the proof the user is asking to delete a user account for which the user has access. If the user profile is not changed as reported, the Stack Exchange team doesn't proceed with the account deletion.