He dislikes whiny students and Friday nights. Though he is being incredibly unsatisfied with his job and often trying to seek a new one (only to return later), he wants to have a life-changing effect on his students. The impression may have been left a bit differently than he may have aimed, as there is graffiti of him as a fire-breathing wolf above one of the water fountains in the school. He may be a history teacher, though Esmargot said it was a math class ("Diary of a Lost Fish"). As frustrated as he is with his students from time to time, he still cares about them, and sometimes takes parental approaches to disciplining them, such as calling students by their full names when they are misbehaving ("Happy Birthfish, Jocktopus", "Brothers' Day"). He sometimes becomes empathetic with them, understanding Milo's declaration of Brother's Day with his own desire to have one brother, rather than eight older sisters, in his youth. Even though he never knew he could get pregnant, he seems to have accepted it quite well, especially after revealing it to the class, and is even open about it from time to time.
He seems to have a mild artistic streak, as he sometimes draws on the chalkboard during his lectures.
According to Milo, his nose looks like a giant sea cucumber.
He spotted Bea sneaking into Clamantha's locker so she could get the yearbook picture. When the Grow-Dino grew and exploded inside, he simply just said "works for me" ("Bea Stays in the Picture"). It is shown that Mr. Baldwin sleeps during the job. He made a lecture on the history of lectures. He then quickly fell asleep in the middle of the lecture ("Fish Sleepover Party"). Mr. Baldwin does roll call every morning, and can't stand Milo's entrance with the eel. Mr. Baldwin says it can't be about him all the time. He then reveals he's pregnant and never knew male seahorses could get pregnant ("Fish Out of Water"). He caught Jocktopus beating up Albert and called him by his full name. He gave Albert detention for standing in the hallway too long ("Happy Birthfish, Jocktopus").
When Bea went on a plane and crashed the ceiling of Freshwater High, Mr. Baldwin yells "Take me with you. I need a new job!" He later made a job in Fish Flakes Inc. when he heard there was a job opening ("Bea Becomes an Adult Fish"). When Mr. Baldwin did a lecture about Shellington, Milo was causing several distractions. When Baldwin could not take it anymore, he told Milo to see him after class. He put him in a bag full of water and tells him he's failing class. Milo assumes him to be joking. Milo heads off, leaving Baldwin annoyed and dumbfounded. When it was time to take the test, Mr. Baldwin notices Milo isn't in his desk. When Milo barely passed the test, Baldwin was as overjoyed as Milo, as he would not have to hold him back another year and "lose anymore hair due to stress" ("Fail Fish"). When Oscar laughed at Mr. Baldwin's lecture when Milo told him to laugh at everything, Mr. Baldwin gave him detention ("Funny Fish").
Mr. Baldwin once took Oscar's backpack and when he heard trouble, he tells his students he has "car trouble". When Milo thought Baldwin was Captain Aquarium, he, Oscar, and Bea (who needed a story for journalism) spied on him to see if he was a superhero. At first, the book says Captain Aquarium heads off to the Eyeglass store to fight crime, but Mr. Baldwin just got new glasses. Then it says Captain Aquarium goes to the bank and fights criminals, but Baldwin runs away when he sees them. Then it says Captain Aquarium changes in a phone booth, but Baldwin napped there. They still didn't give up and Milo had a plan. Bea led Mr. Baldwin to Oscar dressed as a villain and Milo trapped in a glass cup. Baldwin didn't fall for it and was about to take Milo and Oscar home. But Bea flashed her camera and Baldwin accidentally let go of the cup. However, the gang escaped the sharks, as they were vegetarians, and Mr. Baldwin helped Bea pass Journalism ("Baldwin the Super Fish").
Milo's ninja trapped Baldwin in a bowl cause he was about to give a surprise pop quiz to everyone. He complained and said he needs a new job when he gets out ("Milo Gets a Ninja"). Mr. Baldwin once did a drawing of a robot fighting a dinosaur in the board, but it's interrupted by Albert's coughing. Baldwin then noties Albert has the dropsy, so he hits a button, and Principal Stickler and Nurse Fishington comes and put's Albert in a bag. When Milo was faking having the disease, Mr. Baldwin comes with presents and runs away to avoid getting infected ("Dropsy!"). When the Swirlies was on, Mr. Baldwin wanted tickets and asked his students if they have any, even giving them an A for the semester if they give him tickets. Albert stood up, but it was just his birthday and he was going to hand out cupcakes. After Bea, Mio, Oscar and Albert got out of the toilet in the Swirlies, the whole stadium booed and Mr. Baldwin came down floating in an umbrella complaining it took so long to find tickets and Bea ruined it ("Fishing for Compliments: The Albert Glass Story").
When Milo turned giant and smashed Mr. Baldwin's classroom wall, Baldwin said "I'm not even gonna turn around", and drank his coffee. When Milo turned EXTREMELY giant and tried to climb the tanks to Freshwater High, he passed Mr. Baldwin's apartment room. The moment Mr. Baldwin saw giant Milo, he froze in shock and his hair fell off ("Big Fish"). Mr. Baldwin didn't read the chapter of the day so he had no idea what to do for the next 37 minutes. But Principal Stickler came to the room and told Baldwin to stop teaching so he could give the class an important announcement. Baldwin was extremely happy to leave the room and told the class if anyone needs him he will be wandering the halls ("Fish Floaters"). When Milo went out for Peopleing, Bea suggested Milo some other cool role model. She suggested a fish teacher, and they saw Mr. Baldwin sucking algae off gravel ("Peopleing"). When Milo went crazy for recycling, he took off Mr. Baldwin's glasses while he was driving, causing his car to crash ("Legend of the Earth Troll"). Mr. Baldwin didn't say anything when Milo was poking him to see if he's infected with Fish Brain Parasites. Baldwin didn't react because he was silently waiting for Milo to stop and just go away. Baldwin and the rest of the students evacuated the classroom when Milo sucked out all the water in the tank ("Parasite Fright"). Mr. Baldwin was sleeping on the bench when Milo invited him to a "Cinco De Milo" party, which was actually a plan to lure everyone away from the tanks. When everyone figured out Milo's plan, Mr. Baldwin pointed out that Milo broke the tanks while they were at the party ("Pamela Hamster Returns").
When Milo asked Mr. Baldwin why male seahorses could get pregnant, of course, Baldwin didn't respond. Mr. Baldwin was shown to be insane, like the other students, when the cafeteria was closed. Since they were all hungry, Mr. Baldwin yelled out that Finberley found food, causing everyone to chase after her ("Good Morning, Freshwater"). When Bud was cleaning the tank that includes the Freshwater classroom, Mr. Baldwin told everyone to escape, and threw Clamantha in the tank afterwards to see if the tank was clear ("Diary of a Lost Fish"). When Milo figured out Oscar needed to go to a club, and that Clamantha needed someone to be in her cheer club, Milo got distracted by Mr. Baldwin's balloons ("We've Got Fish Spirit"). When the class went on a field trip to Pupu Goodtimes Amusement Park, Mr. Baldwin was shown to hate chaparoning field trips, and told the students to bother him only if it's an emergency. When Mr. Baldwin was about to go on the Pu-Panator, the ride attendant told him that pregnant seahorses aren't allowed to ride ("Good Times at PuPu Goodtimes").
Mr. Baldwin was teaching another boring lecture, then Principal Stickler came into the classroom and said there's a lobster attack. Mr. Baldwin started panicing, only to find out that Principal Stickler was just kidding. When Mr. Baldwin got startled, he told Stickler that that wasn't a nice thing to do to a man in his condition, due to him being pregnant. When Mr. Baldwin was taking attendance, he came across a couple of student's name that starts with an "O", and Oscar came to school just in time for his perfect attendance award ("Run, Oscar, Run"). Mr. Baldwin was shown to be really bored, and even slept at some points in the "Potatoes for Winter" play. When the play was over, Mr. Baldwin was still sleeping, eventually waking up, glad that the play is over ("Fish School Musical"). Mr. Baldwin gave Milo and Oscar all of his money for a hat so Milo and Oscar can stop begging him to do so. He then ran away from the store, screaming. At the dance, Baldwin gave Ms. Lips the hat that he bought, and said "what a doll" when he was watching he skip to Freshwater, suggesting a crush on on her ("Employee Discount").
When Mr. Baldwin got Steve Jackson's hair gel all over his hair, he showed it to Milo, Oscar, Albert, Jumbo, and Steve Jackson. Only they seemed really disgusted by Baldwin's hairstyle ("Hairanoid"). Mr. Baldwin received Milo's Christmas invitation when shoveling off his driveway, only for Mr. Mussels and Coach Salmons to zoom past him, causing the snow to plow over his car. Bea and Milo delivered Baldwin's present to his house, causing Baldwin to wake up the second they leave, thinking they are "intruders" ("Merry Fishmas, Milo").
Mr. Baldwin shows dislike towards Milo and doesn't appreciate him. Mr. Baldwin thinks of Milo as a "selfish fish" and also thinks it's annoying how Milo always interrupts the class when it's "learning time" ("Fish Out of Water"). As much as he is irritated with Milo, he cares about his welfare, and shows great concern for him (and himself) when he is failing the class, as well as making an effort to rescue him while falling from the edge of a shelf ("Baldwin the Super Fish"). He loses hair cause of stress teaching Milo ("Fail Fish").
Mr. Baldwin may have a close friendship or even a crush on Ms. Lips. In "Employee Discount", he gave her a hat that he had bought from Milo and Oscar. At the same time, however, he responded to her remarks during Potatoes for Winter ("Fish School Musical") with the utmost sarcasm, due to his displeasure of being there.
- He is voiced by Dana Snyder, who also voices Bud and Clamantha's mom.
- He commonly sleeps on the job.
- He is the first Disney Channel male character to deal with being pregnant.
- He has yet to give birth.
- He never knew that male sea horses can get pregnant ("Fish Out of Water"). In spite of this, he seems eager to become a father.
- In "Baldwin the Super Fish", it is seen inside his room a bassinet for his babies with a crib mobile over it.
- He has a "Baby aboard" sign on his car windows.
- His car license plate is "PREGDAD1" ("Legend of the Earth Troll")
- He is having quadruplets and all of them are girls ("Spoiler Alert").
- He has a best friend named "Mark" ("Dropsy!").
- Milo said during his class that his nose looks like a giant sea cucumber ("Fish Sleepover Party") which is odd because one of the Freshwater High cheerleaders appears to be a sea cucumber ("Underwater Boy", "Parasite Fright").
- He has a "Panic Button".
- Mr. Baldwin hasn't been out of his house on a Friday night since 1986 ("Baldwin the Super Fish").
- He seems to be in love with Ms. Lips ("Employee Discount").
- He has a very strict "no sleeping in class if he doesn't get to" policy. If he doesn't get to sleep in class anymore, his students don't get to either. ("Milo and Oscar Move In")
- He has eight older sisters ("Brothers' Day").