Who was in charge of the shire and acted as both a police officer and judge?

The shire reeve, historically, served as the chief magistrate and law enforcement officer of a shire, which is a historical term for a county. As a shire reeve, this individual had the dual responsibility of maintaining law and order while also presiding over legal matters within the community. This role included duties such as overseeing the local court system, enforcing laws, and addressing criminal activities, which made the shire reeve a central figure in both judicial and law enforcement capacities.

In contrast, the other roles presented do not encompass both judicial and law enforcement responsibilities to the same extent. A county executive typically oversees county government operations, while a local constable focuses primarily on law enforcement without judicial authority. The tax collector's role is strictly financial, managing the collection of taxes and not involving any law enforcement or judicial functions. Thus, the shire reeve's unique combination of responsibilities makes this answer the most appropriate choice.