A well pumping system can include an actuator that reciprocates a rod string, and a rod rotator including at least one helical profile and at least one engagement device. The rod string may rotate in response to longitudinal displacement of the rod string while the engagement device is engaged with the helical profile. A method of rotating a rod string in a well can include rotating a rod in a rotary direction, in response to displacement of the rod in a longitudinal direction, and preventing rotation of the rod in an opposite rotary direction, in response to displacement of the rod in an opposite longitudinal direction.