Hershel Greene wasn't always a farmer but after the death of his wife he decided to follow the family career by moving back to the farm. He is a farmer before the start of the zombie apocalypse and continues that role even at the worst of times after the zombie outbreak. Hershel did have children, 4 daughters named Maggie, Lacey, Rachel and Suzie and 3 sons; Shawn, Billy and Arnold. Once Shawn was bitten by a zombie Hershel refused to believe that his son was gone, so from then on he locked zombies into his barn thinking they were just sick humans that could be cured in the future instead of just killing them off.
Hershel was created by Robert Kirkman, his first appearance was in Image Comic's The Walking Dead #10.