PHP would not be where it is today without the help and effort of thousands of people. A particular few deserve special mention and thanks - if you see them around at a conference, buy them a drink!
PHP was originally created by Rasmus Lerdorf, and he oversaw production of the first release and PHP/FI 2.0. PHP 3 was rewritten from the ground up by Zeev Suraski and Andi Gutmans, and the three of them are the "language architects" behind PHP.
In the PHP group, the developers who primarily work on development of the language core, there are: Thies C. Arntzen, Stig Bakken, Shane Caraveo, Andi Gutmans, Rasmus Lerdorf, Sam Ruby, Sascha Schumann, Zeev Suraski, Jim Winstead, and Andrei Zmievski. Each of them has worked exceptionally hard, along with the help of many others, to put PHP where it is today.
If you have a little time on your hands, visit http://www.php.net/credits.php and read the full credits online yourself - you will see that PHP really is a community effort built by the collective desire to build the best language possible.