A TEAM OF THREE
All countries have a "head of state" and a "head of government". In some political systems the president is the head of state and the head of government. In other countries, the two roles are separated. Sometimes the head of state is a president, but in all constitutional monarchies, the head of state is the monarch. The head of government is the Prime Minister. He or she is elected by the people and controls day to day government operations. This separation of powers is designed to prevent one person from having too much power.
New Zealand is fortunate because, as a Commonwealth Realm, it has a Governor-General. The Governor-General is neither head of government nor head of state. Often he or she is referred to as the "de facto head of state" which means that he or she operates like a head of state, but isn't legally one. Because we have a Governor-General, we can divide political power between three people, instead of just two.
The Governor-General can keep watch over the Prime Minister to ensure he or she is not attempting anything illegal. The Queen can keep an eye on both to make sure they are doing their jobs. Fortunately, the system works so well that there have been very few cases where the Queen or a Governor-General needed to take action to stop a prime minister from abusing power. It has happened before in other countries, and if it happens here in the future, kiwis can be confident that their democracy is safer in the hands of three people than in the hands of one or two.