Serious Sam is the first video game (released in two episodes) in the Serious Sam series. It is a first-person shooter (with third-person shooter options) created by the Croatian development house Croteam. Originally released for the PC market only, Serious Sam's rising popularity resulted in the porting of the series to a number of different platforms, including the Xbox, GameCube, PlayStation 2 and Xbox Live Arcade, among others.

The series follows the adventures of protagonist Sam "Serious" Stone and his fight against the forces of the notorious extraterrestrial overlord Mental who seeks to destroy humanity.

The First Encounter was the first game in the series; it had been in the making since 1996 and had a video showing its early game play in 2000. The First Encounter was originally developed by Croteam as a demonstrator for their engine and this is the reason why some countries saw its initial release priced at less than half the value of other games in the genre.

The Second Encounter starts where the previous game left off, with Sam traveling to Sirius on the SSS Centerprice. Unfortunately, the starship is accidentally hit by the "Croteam crate-bus" and plummets down to Earth's surface. As the starship falls, Sam reads the coordinates and frets about crash-landing into Egypt again, but instead he crashes into Central America in the Mayan age, with the starship now heavily damaged upon impact.

However, not all hope is lost, since the Sirians left a "back-up starship" on Earth, which was a fail-safe in case if anything ever happens to the SSS Centerprice. However, since this back-up starship is located in a different time and age than where and when Sam is currently in, he will have to uncover the locations of the Sirian portals that will help him reach his destination. With this new objective, Sam storms through Mesoamerica, then travels to Mesopotamia and finally to Medieval Europe where the back-up starship is located.