If we consider the lookout man story in a more general sense, the lookout man is likely the most prominent character. But depending on the nature of the story, there could be other characters that are important. For instance, if it's a story set in a lighthouse, there could be a keeper who is the lookout man's supervisor or a friend. Or if it's a story about a frontier outpost, there could be settlers or soldiers that the lookout man is protecting by being on the lookout.
Since I don't know the exact 'the lookout man story', it's hard to say. But surely the lookout man himself is a main character. There might also be people he reports to, like a captain if it's a ship - related story.
In a typical lookout man story, the lookout man is the central figure. He may interact with other crew members if it's a nautical or military setting. For example, there could be a navigator who depends on the lookout man's information. There might also be a antagonist in the story, such as a pirate or an enemy force that the lookout man is trying to spot in order to protect his own side.