Obviously, Chester 5000 is the central figure in this story. But there could be other important characters too. For example, there might be a human scientist who is in charge of Chester 5000's programming and development. This scientist could play a role in how Chester 5000 approaches love. There could also be another robot or a group of humans that Chester 5000 has relationships with, either friendly or romantic in nature.
In the 'chester 5000 robot love story', Chester 5000 is the main character. It's the robot around which the whole story revolves. However, there could be other characters that are crucial to the plot. There might be a human character, let's say a young woman who works in the same laboratory as Chester 5000. She could be the one that Chester 5000 starts to have feelings for, or she could be the one who helps Chester 5000 understand love better. There could also be other robots in the story that are friends or rivals of Chester 5000, which would add more complexity to the relationships and the overall story.
The main character is likely Chester 5000, the robot. There may also be other characters such as the creators or users of Chester 5000, or other robots or humans that Chester 5000 interacts with in the context of the love story.