VMS Help CREATE, /TERMINAL, Qualifiers, /CONTROLLER  *Conan The Librarian (sorry for the slow response - running on an old VAX)

       /CONTROLLER=filespec

    Specifies the name of the terminal window controller image.
    This name allows the CREATE/TERMINAL command to create a window
    on a variant controller, such as for a language not supported
    by the base product. For a DECterm window, the default is
    SYS$SYSTEM:DECW$TERMINAL.EXE. The device and directory default
    to SYS$SYSTEM and the file type defaults to .EXE.

                                   NOTE

       The "name" field of the file name as returned by $PARSE
       is used to form the mailbox logical name. For example,
       if the file "name" is DECW$TERMINAL, the mailbox logical
       name will be DECW$TERMINAL_MAILBOX_node::0.0. For backward
       compatibility, the controller also defines a logical name
       DECW$DECTERM_MAILBOX_host::0.0 to point to the same mailbox.