What is a person who sharpens things called?

A person who sharpens things, such as knives or tools, is commonly referred to as a "sharpening specialist" or "sharpener." In some contexts, they may also be called a "grinder" if they use grinding tools, or simply a "knife sharpener." In traditional trades, they might be known as a "cutler," especially if they focus on knives and cutting tools.