Tripp Campbell (Logan Miller) is the teenage lead guitarist of Iron Weasel who has always dreamed of joining a rock band. Despite his age, Tripp is the most mature of all the members of Iron Weasel and is determined to help the band make a comeback. Tripp is the only Iron Weasel member of the group that is still finishing school. He usually takes out his anger by playing the guitar, as seen in the episode "I Want to Punch Stuff". He has had a lot of dates and crushes and is allergic to nuts. Tripp is the one who usually solves the band's problems. Throughout the series, Principal Strickland in Season 1 and Principal Jenkins in Season 2 give him detention if he does something by accident, mean, minor, etc. His idol is Derek Jupiter, whom Tripp helped in the episode "Pain Games" to regain his confidence.
Ash Tyler (Stephen Full) is the band's amiable drummer, who is often depicted as being the most childish and simple-minded one out of the members of Iron Weasel. He used to have a pet fish named Sushi (and Sushi 2); both of them were killed after Burger's shorted-out bass zapped it. It is shown that he knows random bits of trivia. In the episode "Slap Goes the Weasel", it is revealed that his real name is Ashley. If someone called him that (like Izzy in that episode), he would go into wild tantrums, in a manner similar to Charles after someone calls him "Chucky". In the episode "Road Tripp" he reveals that he uses 4 kinds of hair gel. In the episode "What Happened", he reveals that his great-great-grandfather wore a pickle suit during the battle at Gettysburg. He seems to be slightly smarter in Season 2.
Burger Pitt (Greg Baker) is the food loving, rather dimwitted bass player of Iron Weasel. He has a very electrified personality as a rock star, and is shown to have a lot of joy in physical acts, such as smashing his own bass or smashing his head into a wall. He is noticeably overweight and has disgusting habits, including eating worms. Burger is known to have a secret crush on Tripp's mom, Beth, and he often sports black nail polish on his fingers. He also won the first Weasel Prank in the episode "Prank Week".
Derek Jupiter (Steve Valentine) is the British, usually selfish, cocky and charming singer. He is known to be a very good magician as shown in episode "Magic Tripp" and is multilingual. Tripp claims that Derek is the heart and soul of Iron Weasel while Vic Blaylock claims that Derek causes all the problems in the band. He is also the tallest of the band and seems to be a little smarter than Ash and Burger. He admits to have his very own dungeon when Ash found an unfamiliar set of keys in "What Happened?". He can also play guitar as seen in "Slap Goes the Weasel", "Road Tripp", etc. as well as key board, as seen in episode "Izzy Gonna Sing" and in several other episodes. He is afraid of snakes and on "Pain Games" he lost confidence in himself after Metal Wolf stole a gig from them. He usually makes fun of Burger and also tells stupid, boring stories from his family that nobody cares about.
Izzy Fuentes (Caitlyn Taylor Love) is one of Tripp's best friends and also a huge fan of Iron Weasel among other rock bands. She is also an aspiring singer and has attempted many times to become Iron Weasel's back-up singer. She apparently doesn't know what a prank is according to the I'm in the Band episode "Prank Week". In the I'm in the Band episode "Izzy Gonna Sing?", she temporarily becomes the band's lead singer when Derek is sick and loses his voice. She was in a band with Tripp called Booger Smack in the third grade as seen also in "Izzy Gonna Sing?". Despite being a main character, she appears almost as a recurring character due to her being absence from many episodes. She is also known to have a crush on Iron Weasel's old lead guitarist (Bleed) in the I'm in the Band episode "Bleed Guitarist".
Beth Campbell (Beth Littleford) is Tripp's loving and supporting mother. She is 41 years old in Season 1, and 42 years old in Season 2 in the prequel series. She has custody of Tripp after divorcing her husband. She regrets having Iron Weasel living in her house. It is revealed in the I'm in the Band episode "Weasels vs. Robots" that she is a dental hygienist and also has a large set of plastic teeth.
Principal Cornelius Strickland (Reginald VelJohnson) is Tripp's hot-tempered former principal who deals with a lot of shenanigans at the school, especially involving Iron Weasel, which he really loathes. He is featured in the first season but reappears as the Superintendent in the episode "Iron Weasel Gets Schooled". His name may be based on Principal Strickland from the Back to the Future. He was promoted to superintendent and was replaced by Principal Maurice Jenkins (Mark Teich) in the second season of the prequel series.
Jared (Aaron Albert) is Tripp's nerdy, exceptionally smart, and odd friend and uses charts a lot. He is 15 years old. He screams like a girl when he gets freaked out. He also has been to a bird calling camp, has a crush on the lunch lady and has a father who builds robots. Jared only appears in the first season of the prequel series.
Ernesto the Besto (Hollywood Yates) is Iron Weasel's former roadie who is now a mixed martial artist. He's gotten pantsed by Iron Weasel a numerous amount of times (including when he was proposing to his girlfriend at a concert and was even arrested for attempting to attack the band after they pantsed him). He eventually returns to get revenge on Iron Weasel for pantsing him, Ernesto and the band eventually makes up, but he gets arrested (and pantsed) again at the end, swearing revenge on the band once more.
Charles "Chucky" Albertson (Zayne Emory) is the 12-year-old (13 years old in Season 2 of the prequel series, 14 in the sequel series, 15 in it's second season, 16 in it's third season, 17 in it's fourth season and 18 in it's fifth and final season) kid who got injured because of the Weasel Slap. He is Simon Craig's new stepson who is mean and disrespectful to the Iron Weasel. He hates being called Chucky because it rhymes with "Sucky" and even goes into wild tantrums after someone calls him that. He also once had a crush on Izzy. He first appears in the episode "Slap Goes the Weasel," and did not appear again until "Chucky's Revenge." He has since appeared in some season 2 episodes of the prequel series.
Simon Craig (Alan Thicke) is Iron Weasel's manager and Charles' stepfather introduced in Season 2 of the prequel series.
Principal Maurice Jenkins (Mark Teich) is Tripp's principal who took the spot Cornelius Strickland had in the first season in the prequel series and dislikes Strickland becoming superintendent. He was introduced in the second season in the prequel series. He is easily agitated by Tripp's behavior and is bothered by Tripp flirting with his daughter Gia.