Atomic is an auto parts company in Grand Theft Auto: San Andreas, Grand Theft Auto IV and Grand Theft Auto V based on the real-world Goodyear where tires is their specialty.
GTA San Andreas
TransFender and Wheel Arch Angels offer Atomic brand custom rims. Wheel Arch Angels also offers an Atomic-themed paintjob for the Flash.
GTA IV
In GTA IV, they make all the tires in the game and some of the headlights.
GTA V
Atomic serves the same purpose as it did in GTA IV but now has its very own blimp in the sky advertising their products.