Radar Vivian is the younger brother (by one year) of Halley Vivian, younger son of Matthew and Olivia, and younger cousin of Sputnik Vivian on the Sprout shows Astroblast and Astroblast: All Grown Up!. Named after Olivia's cousin, Radar Prescott, he was born in The Astroblast Movie (released November 20, 2011). His name means a transmitter. Radar is voiced by Tara Strong. He's 3-4 months old, and likes to call Sputnik "yucky".
Radar Vivian is the youngest member of the babies , and because he is just a infant, his big sister Halley feels that it's her "sponsability" to teach him about things work in the world. Radar has a personalitly of a typical 3-month-old: all id. He wants everything NOW and will do whatever he can to get it. And once he does get it, he won't let go without a fight. Radar will wail inconsolably when frustrated, but he'll immediately stop crying when something else attracts his attention. While his tantrums are often annoying, he has the saving grace of all babies: he's irresistably cute. - Astroblast Description from Sprout.
Radar Vivian has grown quite a bit from the little baby we first saw in The Astroblast Movie, He is now 9 years old, and enjoys wearing bizarre outfits, talking in code and getting any information he can about alien abuctions! His Principal, Mr. Pangborn, thinks Radar is a bit too strange, and almost went crazy himself trying to psychoanalyze what could be wrong with him. Could it possibly be caused by Comet and Venus accidentally dropping Radar on his head when he was a baby? Maybe... Or perhaps Radar is just one of those utterly unique individuals who doesn't try to be weird... he just is! - Astroblast: All Grown Up! Description from Sprout.
Radar joined the Astroblast cast in the year of 2011. From the very beginning, Radar is a monkey, and has always worn light green trap-door pajamas. Because of his age, Radar can't say as many words as the other babies. For the final 5 years of Astroblast's run, Radar had to learn how to be a cooler. He always wants everything at his age, and will always do whatever he can to get an object. He is as selfish as his cousin Sputnik, and when he cries, he will not stop until something or someone will get his attention, but the difference being that he is a baby and will share things with Halley and the rest of the babies.
Most of the episodes that Radar is prominent in usually involves the rest of the babies trying to make Radar more like a "big baby", teach him something, or save him from something. When Olivia was pregnant with Radar, she and Matthew assumed that he was going to be a girl, and had planned on naming the baby "Trixie," after Matt and Matthew's late mother (although her real name was actually "Beatrix," but most people called her "Trixie"), but when the baby turned out to be a boy, they named him after Olivia's cousin, Radar Prescott.
Radar loves his sister Halley dearly as she sticks up for him when others do not. An example is A step at a time when Halley defends him over his walking, saying Radar will walk when he is ready. When Radar sees Halley, he attempts to grab on to the couch and walk but just falls back down. Halley comforts him, telling Radar he will walk when he is ready but until then, Halley will get down to his level and play with him.
Radar always called Jet "Jeb", and in the episode The Jungle, he refers to Comet and Venus "Commey" and "Veneey" respectively. He is a fur puller. Radsr remains the same height until a season 8 episode titled Back To School when he, according to his father, Matthew Vivian, "grew an inch".
In the episode A Dose of Radar, Halley feels left out as the adults are giving Radar all the attention because he got a booster shot in his finger. Halley and the gang decide to find ways to get the attention of the adults because they believe that if they do, they will get lollipops, as Sputnik shows off that she has loads of lollipops. However, by the end of the episode, Halley realizes that she doesn't need to cry for attention anymore because her little brother Radar will always be there to listen to her.
Radar is a monkey with brownish fur and a pair of white eyes with black pupils. The character wears light green trap-door pajamas. Other times he is wearing just a diaper.
In Astroblast: All Growed Up, he wore a blue and green Hawaiian shirt, blue shorts, white socks, and blue and white sneakers. He now has a little of brown hair.
Radar has appeared in many episodes of Astroblast and its spin-off series, Astroblast: All Grown Up! since The Astroblast Movie. He made his debut in the movie, though he was mentioned previously in The Family Tree (in which Olivia, his and Halley's mother, realizes that she is pregnant), and made his final appearance in Golden Boy, an episode of Astroblast: All Grown Up!. It can be also noticed that a main character has been added in the first two Astroblast movies.
- Radar was the first of two new babies to debut in a film, the second being Jade in Astroblast in Paris: The Movie.
- Radar is one in three of the main Astroblast characters to have the camera viewed from inside his mouth in Astroblast: All Grown Up!. The other two are his older cousin, Sputnik, and his pet dog, Bruce.
- In the Astroblast: All Grown Up! episode entitled Brothers Grimm, Radar is seen writing with his left hand, which would imply he is left handed, this would also imply Jet is not the only baby who is left handed.
- Radar does believes in aliens, and doesn't think they're scary.
- As said in the Astroblast: All Grown Up episode Truth or Consequences, Radar was accidentally dropped on his head by Comet and Venus when he was a baby. It is also shown he does know about this. Despite this, Olivia doesn't believe that it is the reason behind his eccentric behavior, rather it is genetic from his father's side. Given Matthew's behavior, she's probably right.
- In one Astroblast: All Grown Up! episode, it is said that Radar is 4 years younger than Halley, this may be a continuity error, or the writers and directors forgot the babies stayed the same age in the show.
- Though there was no episode, Radar was seen as a 1-2 year old, and 3-4 year old in the Astroblast: All Grown Up! episode Truth or Consequences.
- In Jet's Dream, in Astroblast in Paris: The Movie, Radar is seen carrying a flag and running/walking even though he never walks at all in the actual cartoon series.
- Throughout "Astroblast: All Grown Up!", Radar seems to have a connection to higher-power deities. He quickly became friends with Cupid in "It's Cupid, Stupid". He also seems to have connections to aliens as shown in the episode "Halley Foolery" in the very end where he is beamed down back to Earth with a slice of pizza at 5:45 PM so he won't miss his laser tag game. And finally, he became friends with Bean, a ghost from Camp Everwood in the episode "Interview With a Campfire".
- According to the episodes "Brother, Can You Spare the Time?" and "Thief Encounter", Radar is in the fourth grade.
- In "Brother, Can You Spare the Time?", it is shown that Radar can't get along with his fellow fourth grade peers.
- In "Brother, Can You Spare the Time?", it is revealed that Radar believes the Earth is triangular.
- In the episode "Ladies' Man", Radar created his own language called "Radganeese".
- In "Rachel, Rachel", Radar invented his own religion called "Radar Vivianism".
- In "Tweenage Tycoons", Radar shows that he doesn't like to let Halley down as he continued to help her as well as their friends, by making inventions for them so they could have money to get tickets to see The Sulky Boys concert.
- In "Golden Boy", Radar can speak to fish and leeches.
- In "Lucky 13", Radar can speak to dolphins.
- It is revealed in "Golden Boy" that Radar has a clapper switch to turn his room lights on and off.
- So far, despite being such a prominent character in the later years of Astroblast, Radar hasn't yet appeared in the Boom! Studios comic.
- Like Halley, Radar is Jewish as Judaism is spread through the mother's line.