copy-marker is a built-in function in `C source code'.

(copy-marker &optional MARKER TYPE)

Return a new marker pointing at the same place as MARKER.
If argument is a number, makes a new marker pointing
at that position in the current buffer.
If MARKER is not specified, the new marker does not point anywhere.
The optional argument TYPE specifies the insertion type of the new marker;
see `marker-insertion-type'.