Most of the time, Gerald comes across as a cool, friendly, easygoing, and very supportive and helpful to his best friend.
At school, Gerald is the class president and considers himself very cool, and apparently, so do his friends. When it was revealed that Arnold was on Rhonda's so-called "Cool List", and that Gerald was on her other list known as "The Geek List" (due to a grudge Rhonda had against him over running for class president), many classmates were surprised to find this out. He can even become jealous of others if they steal his spotlight, which likely stems from his home life, where he is the oft picked on middle child.
He often serves as the voice of reason in the group of fourth-grade friends, and a realistic counterbalance to Arnold's optimistic attitude. This sometimes causes conflict between the two, but never for long. Another facet of Gerald's personality that opposes Arnold's is his weaker sense of morality. Gerald is far less open to helping others, and almost always attempts to dissuade Arnold from doing so. He's also more likely to doubt people or to spite somebody that he believes has wronged him, such as his brother. He's also somewhat selfish, seen when he hesitated to tell Jamie O that his girlfriend was manipulating him in order to get benefits from him.
Gerald is of African-American heritage, and his most distinct features are his hi-top fade (classmate Helga often calls him "Tall Hair Boy"), and his red shirt with the number 33 on it. As a child, his redshirt simply said "3". He also wears blue jeans and red and white high top sneakers.
In The Jungle Movie, he wears a red hooded sweatshirt with the same number on it, and different high top sneakers of the same color with white laces. He resembles his brother Jamie O more closely, as his haircut is now a taller version of Jamie O's, and the shape of his head is now less circular, and more similar to his brother's.
He serves the role of the storyteller in the fourth-grade group, and his tales are often the setup of the urban legend episodes. He sometimes delivers the urban legends in the form of jazz poetry, which he also recited on stage at the Coco Hut. Gerald's flair for performance has also manifested musically, such as in the episode "Gerald's Tonsils", Gerald is a soloist of a chorus, in "Partners", he plays the piano, and in the episode "Arnold as Cupid" he's briefly seen playing the violin.
He notably possesses a lot of information and know-how on Hillwood and its residents, some of which provided by his mysterious friend Fuzzy Slippers.
He developed a fear of riding a bike after he accidentally rode down the steepest hill in the city, and crashed when he was small. However, Arnold helped him overcome his phobia, and win the city bike race.
- Timberly Johanssen — Gerald's little sister. She is usually causing trouble due to her desire for attention or naturally childish behavior. Unlike all the other children on the show, Timberly seems to get older throughout the series: At her first appearance, she is mentioned to be four years old, but she already attends the first grade in "Timberly Loves Arnold".
- Jamie O Johanssen — Gerald's older brother, who while he causes trouble for him, ultimately cares for him, their relationship becoming more amicable after the events of "Jamie O in Love " after Gerald helps Jamie O see his girlfriend is just using him. They have a typical brother relationship- Gerald tends to annoy Jamie O or just wants to be around the older crowd, and Jamie O teases or pulls pranks on his little brother.
- Martin Johanssen — Gerald's sometimes strict war veteran father, complains about wasting electricity. He loves his family though and looks out for them. Gerald doesn't think he's a real war hero, his father saying all who go to war are heroes, no matter their role or what they did. However, Gerald learns Martin actually did save someone during the war, making him proud of his dad.
- Mrs. Johanssen — Gerald's very kind mother, keeps the family together. She doesn't get as many lines or scenes as the rest of her family
- According to one of Craig Bartlett's Hey Arnold! comics, Gerald has a bald uncle named Maurice.
- Arnold Shortman - Gerald's best friend whose relationship dates as far back as pre-school. The pair has a distinct handshake consisting of putting two-thumbs-up fists together and wiggling the thumbs back and forth.
- Phoebe Heyerdahl - Gerald's classmate, who it was strongly suggested he had a crush on throughout the series, which she reciprocates. Main article: Phoebe and Gerald
- Connie — A sixth-grader who was Gerald's "date" at the school dance in "6th Grade Girls", but it turned out that all she wanted was to make her boyfriend Burt jealous. She was the first girl to kiss Gerald.
- Chloe — an older girl who recently moved into the neighborhood, who hung out with Gerald, but only to get closer to his older brother Jamie O. Gerald felt betrayed after the truth was revealed.
- His hair looks similar to Marge Simpson's from The Simpsons.
- Gerald was voiced by Jamil Walker Smith throughout the entire run of the original series, even as Smith went through puberty. The voice change was explained as a side effect of when his tonsils were removed, and from that point on, Smith's voice was digitally mastered to a higher pitch by using sound audio. Hey Arnold! The Jungle Movie is the first and only time Gerald has a new voice actor. He sounds noticeably more youthful in it (similar to his Season 1 or 2 self) as a result.
- Gerald's last name is spelled "Johanson" in the first season and "Johanssen" in the second season, although it's spelled "Johannsen" in the credits for "The High Life" and "Johansson" in the credits of the "Urban Adventures" tape. Since Gerald signs it "Johanssen" in "The High Life", that's the spelling used in this wiki.
- It has often been speculated that his shirt featuring the number "33" is a reference to Chicago Bulls player Scottie Pippen. However, Craig Bartlett claims that this is only a coincidence.
- Gerald seems to have figured out Helga's feelings for Arnold at some point before Hey Arnold! The Jungle Movie.
- Despite being just 9 years old at the time, Gerald is shown to be quite proficient at driving a vehicle with a manual transmission in Hey Arnold! The Movie. This is first shown at the beginning of the movie when he is playing a video game called "Runaway Bus" at the arcade, and towards the end of the movie when he is forced to take the controls of a real city bus in order save the neighborhood.
- He's only the deuteragonist who is the best friend of Arnold. This role doesn't go to Helga because she was the overarching antagonist and tritagonist which separates her from the other main characters, but actually was Arnold's girlfriend and arch-rival.
- "Phoebe and Gerald: Lovers in the Background" published by Shieldmaiden56 on "Hey Arnold! – A Critical Analysis"