tramp-default-user-alist

tramp-default-user-alist is a variable defined in `tramp.el'.
Its value is 


(("\\`smb\\'" nil nil)
 ("\\`\\(?:fcp\\|krlogin\\|nc\\|r\\(?:cp\\|emcp\\|sh\\)\\|telnet\\)\\'" nil "artur")
 ("\\`\\(?:ksu\\|su\\(?:do\\)?\\)\\'" nil "root")
 ("\\`\\(?:socks\\|tunnel\\)\\'" nil "artur")
 ("\\`synce\\'" nil nil))

Original value was


Documentation:
Default user to use for specific method/host pairs.
This is an alist of items (METHOD HOST USER). The first matching item
specifies the user to use for a file name which does not specify a
user. METHOD and USER are regular expressions or nil, which is
interpreted as a regular expression which always matches. If no entry
matches, the variable `tramp-default-user' takes effect.

If the file name does not specify the method, lookup is done using the
empty string for the method name.

You can customize this variable.