Changing default owneruser to someone who doesn't exist

[tozz]

By default this is 0:0 but if I want to change it to a user who doesn't exist?
Lets say I want to be the user ftp from the group ftp but I don't want this user to be available.. or how do I at leas disable this to user to login at all?

[darkone]

add user without ips + set password to random blurp.