Adrian Rossouw has been a Drupal core developer for over 5 years (since January 2003) and has contributed several important components to the Drupal ecosystem.
He is responsible for (among other things) :
PHPTemplate and the template engine abstraction layer
Design and implementation of the Drupal Forms API.
Initial design of the install API
Integration of multi-site into Drupal core
Maintained the PostgreSQL port of Drupal for over 2 years
Original author of the Buddylist module.
In 2004 he co-founded Bryght, becoming one of the first Drupal developers to start a Drupal-oriented services company and also one of the first developers to earn a living doing only Drupal.
While at Bryght, he developed a hosted service to host and maintain thousands of Drupal sites through an automated hosting system. This system forms the basis for the Ægir site management system, being developed by Raincity Studios (who acquired Bryght in 2008).