He and his dad have a good father-and-son relationship. His dad tells him what he should do when something's wrong in the house and he also likes to spend quality time with his only son like going fishing and encourages him to do a lot of chores as exercises.
He and his mother have a fine mother-and-son relationship. Despite having a further relationship than with his father, he really respects her more because he is really scared of her getting upset and doesn't want to see her doing anything wrong.
After they just have met and collided against each other, Fred had gained absolute control over him that he can't refuse and will obey to him only. They are the best buds who like to play games and fight aliens, even at the same time.
She is the only friend of Fred's that is a girl and also a close neighbor just next door. She thinks of Fred as boy who is too childish of fun and games and a waste of time, however, there are times that she is mistaken that it isn't bad being him that way. When the Earth is under attack by invaders, Agent Brains comes into action and Fred comes along because he has Friday and can command him to help.
He's been close friends with his former best friend (Friday being the current). However, he still maintains his friendship and hangout with him as usual. With the exception of alien activities and Braianna's secrets, he can entrust him with anything. Just to know that it would endanger his friend from harm's way.
He's been close friends with him since childhood and had been hanging out with him and the others during lunch, after school, weekends, etc. Though not being the most helpful friend and sometimes childish with his innocence, he usually just ignore him by knowing that his friend is just trying his best to help.
He's been close friends with Eddie though at the same time as a love rival for Nora. Sometimes he envies Eddie being talented and popular in school which has gotten the interest of Nora, thus, he would have to compete against him in someways to get Nora's attention. but as a friend, he doesn't really hate Eddie, he just doesn't like him being close to Nora.
Gelatina is one of his few alien friends, being a "cute little alien blob," he has a liking to her transformation ability (similar to Friday's) and thinks she's awesome.
He has an unusual relationship with the local school bully Wally K. Though considers him the number one enemy in school, he somewhat doesn't have any sign of hatred towards the bully. He is just actually afraid of getting beaten up and is the only boy who has seen Wally's softer side.
Nearly non-existent, Brains's dad has his faith and trust on him on protecting the Earth while her daughter is away spending time with him or sick at home. However, both Fred and the Super Commander didn't met (not until Episode 20 and Episode 27) and doesn't know much of each other but still they had a good conversation and are cool with each other.
He is neutral to Mort. For him, Mort is just a thorn to his side and his friends' and more of a threat to Agent Brains' secret identity and Friday's existence. He usually mocks Mort for being less popular than him and rarely interacts with.
He has a crush on Nora, probably since the first time he saw her even to the point of making 4637 secret love letters. When both of them have a conversation, Fred starts talking crazy and is like being mesmerized by her charm when asked by a favor. Though he can't control himself when close to her, he continues to impress her with his cool.
He has somewhat a liking in Iria. The way he looks at her makes him think of Brains being well-dressed and a girl he would love to sit next to.