JACKSON, Miss. — Only three people who had ever met this man, Robert Gray, knew that he was running in the primary for governor of Mississippi.

There were the two volunteers who took his $300 filing fee and qualifying papers several months ago at the state Democratic Party office and the candidate for agriculture commissioner who happened to be in the headquarters at the same time.

Otherwise, no one — not even Mr. Gray’s mother, with whom he lives.

At least she voted for him when she saw his name on the Aug. 4 ballot. Mr. Gray, 46, a round-faced, soft-spoken long-haul truck driver who lives on a quiet country road south of Jackson, was too busy working on his rig to vote himself. He would, nonetheless, go on to win, taking 79 out of Mississippi’s 82 counties.

Mr. Gray beat two other candidates, who unlike him spent money and campaigned. Democratic Party officials were stunned. The news media was stunned. Mr. Gray, now Mississippi’s Democratic nominee for governor, gave some interviews and then set off with a truck full of sweet potatoes for a potato chip factory in Pennsylvania.