There's a long history of law enforcement in Sheriff's family. His father was a traffic cop. His aunt, 2 cousins on his mother's side and his little brother...even his grandfather was a traffic cop who directed traffic at Times Square in New York around the turn of the century. Sheriff always knew he too would be a cop. After all, how many other options did he have with a name like Sheriff?
Sheriff is the local law enforcement and the keeper of the peace in Radiator Springs. He takes his job very seriously. Sheriff enjoys telling stories and taking the occasional nap behind the Radiator Springs billboard. That's where he was when Lightning McQueen first zoomed into town years ago, which led to a messy car chase that didn't end well. These days, Sheriff welcomes the hotshot racer Lightning home to Radiator Springs with all four tires.
In the film, he watches McQueen leave for the World Grand Prix. When he is called to London by McQueen he aids McQueen and Mater in fighting the Lemons by chaining one of them up just like he did to McQueen in the first film.