Serious Sam isn't as old as the forerunners he is obviously based on, first appearing as recently as 2001, but his breeding goes back way further. The character himself – Sam "Serious" Stone – could double for Duke Nukem with a bit of peroxide, and the story is as paper thin as they come. Take a little bit of Terminator, throw in some Stargate and you're just about there, in the future an alien menace threatens to over run the human race, but it turns out it's not the first time they've visited us. So Sam is sent back in time to ancient Egypt, the place of the first incursion, to wipe them out and save the future. Who cares about story anyway? It's just an excuse to shoot relentless hordes of alien scum and save the world.