A reeve is a manager of someone's estate or farm. This reeve is also a carpenter, which leads to trouble when the Miller tells a tale insulting carpenters, but most of the Reeve's portrait focuses upon his role as a manager, which he's been doing for many, many years. As an experienced manager, he can estimate the yields of his master's crops and livestock based only on the rainfall from year to year. So good is the Reeve at the reckonings that the people with whom he works, like shepherds and farmers, are too afraid to attempt to cheat. Not so the Reeve himself, though: we learn that he steals from his lord's property only to loan to the lord from these ill-gotten funds, thereby gaining himself favor. Like the Manciple, then, the Reeve is financially outsmarting his masters.
Physically speaking, the Reeve is a bit, well, sickly. He's so skinny that his legs look like straight sticks, and he's "colerik," or diseased looking. He wears his hear cut close to his ears like a priest's, and wears a cloak that looks like something a friar would wear. He's mounted on an able, dapple-gray horse and wears a cloak of blue, both signs of his financial success.