Serious Sam is a video game series created and primarily developed by Croteam. It consists predominantly of first-person shooters. The series follows the advances of mercenary Sam "Serious" Stone against Mental, an extraterrestrial overlord who attempts to destroy humanity at various points in time. The first game, Serious Sam: The First Encounter, was released for Microsoft Windows in March 2001. Several spin-offs were developed by other developers, such as a Palm OS conversion of The First Encounter by InterActive Vision, Serious Sam: Next Encounter (on GameCube and PlayStation 2) by Climax Solent, and Serious Sam Advance (on Game Boy Advance) by Climax London. All three were published by Global Star Software.