The driver was responsible for helping the crew escape while pulling an ill-fated heist at the Bobcat Security bank in 2004. He was waiting just outside the bank's rear entrance in a Rancher XL. As they started driving away, a Police Roadcruiser appeared behind them in hot pursuit, shooting at the car. The driver was shot in the head during the police chase, and Michael pushed his lifeless body out of the left door before taking the wheel.
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In a deleted line during the getaway cutscene, Trevor comments on the driver's death by saying "You buy cheap", pointing out the driver's inexperience and low cost which led to his fate.
He is referred to by Michael as "Local Yokel" so this is likely that he never pulled a score with Trevor, Michael and Brad. This is further supported by a removed line from Trevor calling him cheap.
This is likely that Brad disliked, or even hated him since he called him a "dick" after his death.