It's based on the real-world company Goodyear where tires is their specialty.
GTA San Andreas
In GTA IV, they make all of the car tires in the game and some of the headlights.
Atomic serves the same purpose as it did in GTA IV but now they have their very own sponsorship blimp in the sky advertising their products.
Pre-ordering GTA V will grant access to the Atomic Blimp via a phone call to Atomic.