The noun reaper refers to a person who harvests crops. If your part-time job involves harvesting corn by hand, then you're a reaper. Reaper can also refer to a piece of farm equipment used to harvest crops, especially grains.
It's not a coincidence that reap looks a lot like the word ripe. When the crops are ripe — in Old English, "ready for reaping, fit for eating" — a reaper, either human or mechanical, can harvest them. Reap means "to cut grain with a hook or sickle." This might remind you of the Grim Reaper, the personification of death in art, movies, and stories, who is shown carrying a sickle and is said to be the harvester of souls.