The spinoff film series, Predator, began in 1987, eight years after the release of the original Alien film and just a year following the second film. These two worlds originally met in a 1989 comic book series, Aliens vs. Predators, published by Dark Horse Comics.
The crossover films didn’t come out until more than a decade later, with Alien vs. Predator (2004) and Alien vs. Predator: Requiem (2007). None of the plots from the original Alien series references these crossovers.