IANAL
If the original author contributed any of the code in this file (you copied one of his files and modified it, for example), then both should be credited. If you wrote all the code, your name is all that's needed.
You should conform to the project template, but normally you'd include something like:
* Released under the GNU General Public License
'GPL' is not really as precise as it should be. You might need to specify the version, too. See the license (Version 2 or Version 3) itself for details. As it stands, it could theoretically be released under GPL Version 1, though that's unlikely to be what anyone had in mind (but lawyers would not find any problem with assuming it).
The GNU GPL Version 2 suggests (at the end, under 'How to Apply These Terms to Your New Programs'):
one line to give the program's name and an idea of what it does.
Copyright (C) yyyy name of author
This program is free software; you can redistribute it and/or
modify it under the terms of the GNU General Public License
as published by the Free Software Foundation; either version 2
of the License, or (at your option) any later version.
(and two more paragraphs).
