watcher

A watcher is someone who observes or pays attention to something or someone.

When we talk about a watcher, often we mean a person who keeps an eye on something important, like a security guard watching over a building at night. But sometimes it can also be someone who follows a sports team's performance or a fan of a particular band, always keeping up with their latest news and updates. We might even use the word to describe someone who observes wildlife in nature, trying not to disturb them as they do their job – watching animals in their natural habitat.