They were a pair of Scottish criminals who operated in Edinburgh in the early 19th century. They would dig up newly-buried bodies and sell them to medical schools for dissection.
It's important to note that their actions were not considered morally wrong at the time, as the supply of cadavers for medical education was extremely limited. However, their methods became increasingly gruesome, as they began to murder their victims to acquire their bodies. This eventually led to their capture and Hare's subsequent plea bargain, which saw him become a witness for the prosecution against Burke.