Steven "Steve" Barkin (commonly referred to as "Mr. B") is a substitute teacher at Middleton High School, which is attended by Kim Possible and Ron Stoppable. For reasons of frequent injuries, sickness, or vacation among other staff members, Barkin teaches a variety of classes, ranging from gym to home economics, leading to him being dubbed the school's "permanent substitute" by the show's staff. Unlike most fictional teachers in "high school hero" franchises, Barkin is fully aware of Kim's missions and has, by accident or design, become personally involved in several of them.
Little about Barkin's history, prior to Season 1, has so far been revealed. His father's name is Franklin. It is known that he attended military school as a child and that he served as a Lieutenant in an unidentified military conflict (most likely the Vietnam War), where he was stationed "ten clicks north of Jai Alai," during which time he learned how to cook. It is also known that Barkin has been a teacher in Middleton since at least the time that Kim and Ron were in 9th grade. It is implied that he has been there much longer.
During "Graduation", the last episode, he mentioned that before his own graduation he was a "big man on the football team", "dated the most popular girl in school", and even "helped save the world from time to time". That indicated that he had a past somewhat similar to Ron. However, for some strange reason, it didn't go right for him and was probably what makes him so mean and possibly bitter.
Barkin's manner is analogous to a military drill instructor, typical of most PE teachers in most Western cartoons and one Japanese anime, School Rumble. It is also strikingly similar to the personality of the sergeant of the Smile Away Reformatory School from Phineas and Ferb (who, interestingly, cuts the hair of all his newly introduced students to a style almost identical to Barkin's), exclusively in the episode "Phineas and Ferb Get Busted!". As such, he is a gruff, no-nonsense character who is quick to anger, and who has little to no sense of humor. He is typically abrupt and abrasive with students and is a stickler for punctuality and proper decorum.
Barkin tends to be skeptical of things that he does not understand, especially when the explanation goes over his head. For example, while grading science experiments, he commended two students for building the classic volcano out of vinegar and baking soda, but cast extreme doubt on a device capable of tearing a hole in the space-time continuum. He ended up activating the device and unwittingly releasing a genetically-engineered dinosaur that had been trapped in the rift earlier in the episode.
Barkin's personality has brought him into conflict with the show's protagonist on a number of occasions, primarily when he believes that Kim's missions or social life are encroaching on her school work, or when he feels that she has not been paying attention. He has also been shown to be particularly harsh with Ron, whose laid back personality conflicts with his own, and has been known to pick him up by the lapels and shake him in frustration. Despite this, Barkin tries to take a "tough, but fair" approach. He doesn't play favorites in his classes and will give "credit where credit is due," regardless of what he thinks of the student at other times. Additionally, while Barkin typically likes to be in charge, he has also been shown to defer to others quickly, and without argument, when he recognizes that their experience outstrips his own.
He has also been shown to have a more gentle side that includes an appreciation of baked goods, serving as the den-mother ("Brigadier Pixie") of the local Pixie Scouts chapter (although he ran the unit like a division of the United States Army Rangers), and enthusiasm for housewares. It was also revealed that he sleeps with a stuffed teddy-bear.
He is also revealed to have served in a war (presumably the Vietnam War), where he achieved the rank of Lieutenant, conducting himself more like a drill sergeant than a teacher. His military service would also explain his strict no-nonsense attitude. He tends to panic in a major crisis, which indicates that he may suffer from Post Traumatic Stress Disorder (aka shellshock) as a result of some bad wartime experiences. This has made him extremely paranoid, and he often jumps to completely irrational conclusions that usually involve some sort of conspiracy, government or otherwise. He has also been prone to hysteria and in an incident where he was stuck in a crate with Ron he tried to "survive" by getting Ron to dig a hole in the crate with a "shovel" (actually a high heeled shoe) while he plants herbs by harvesting dirt from their socks, he also claims that a cow in the crate is Mr. Barkin, and speaking to a rubber chicken as if it's a radio transmitter.
Barkin is tall with a large muscular build. He has dark eyes and dark hair cut into a neat flattop. Barkin's beard is lighter in color than his hair and grows at an abnormal rate, he has to shave 15 times a day to keep clean-shaven. If he doesn't, he grows a dense stub in only 19 minutes and a thick beard within hours.
Barkin is one of the only characters in the series whose height is actually given. When he was arrested by the fashion police his mugshots were shown. In these mugshots he stands at 6' 1" (185.5 cm), given his height in the mugshot minus the 3" heels that he states he is wearing.
Barkin appears to have a wide range of abilities as a teacher since he substitutes for nearly every class at Middleton High School.
Over the course of the years he had taken on a number of roles traditionally associated with a senior faculty member, including setting school policy, leading pep rallies, making official announcements over the speaker system, and managing disciplinary procedures against students. He also represented the school's faculty during several official cheer squad events and was apparently put in charge of other teachers on school excursions. While his exact position in the school hierarchy is unstated, he is definitely not the Principal, as that office is held by a woman.
Like many teachers, Barkin works part-time, in his case at Smarty Mart, revealing to co-worker Ron that he had worked in the housewares department for fourteen years while claiming his job at the school was "just for the benefits". He has now also been known to be the school's football coach.
As a secondary character, Barkin is often portrayed through his student-teacher relationships with the show's protagonists, Kim and Ron. However, he has also been briefly romantically linked with two of Kim's foes, DNAmy and the temporarily-good Shego.
Barkin's relationship with Ron is often antagonistic. This seems to stem from an incident in the 9th grade where Ron looked at him funny; Ron insisted that Mr. Barkin has had it in for him ever since, a claim that by Barkin's own admission proves true. Such examples of Barkin having it in for him are when Barkin demands Ron hand in homework before the school doors are unlocked, or giving him into trouble for leaving before he dismisses the class even though everyone else has left. Ron had served in detention a few times already by 10th grade. However, there are times where Barkin has come to respect Ron's unique abilities, such as the time where Ron ended up taking over the home economics class, and when Ron helped Barkin's Pixie Scout troop with their cookie sales (although his initial efforts were less than stellar, Ron quickly adapted), and when they rescued Kim and Bonnie from Professor Dementor's lair.
When Ron tried out for the football team at the start of his senior year, Barkin told him that these weren't the tryouts for towel boy. However, in his second attempt, Ron stunned Barkin with his sudden show of skill. This turned out to be the result of Ron's use of Kim's super-suit, and after it was damaged, Ron found he had to rely on his own running-away skills to make it through a game. As a result, Ron set a new rushing record and was allowed to stay on the team, despite cheating to get onto it in the first place. Since Ron got a job at Smarty-Mart, he and Mr. Barkin are now co-workers, and Ron has complained about Barkin's attempt to teach him on Smarty-Mart time.
While Mr. Barkin does not show the same disdain for Kim that he has for Ron, he has often found himself at odds with her, particularly when she attempted to bail on the detention she received for being tardy three times in one month. Barkin generally respects her as a top student but isn't afraid to point out her shortcomings, such as when she hadn't begun her college selection process.
Fans believe that during the ceremony of 'Graduation, Part Two' when Barkin said, 'He's going to miss Kim, she replied that he still had the "tweebs." She also said that he would suffer another four years of school with Jim and Tim. He also chased them after they destroyed his new car (after the first one was destroyed by Tim and Jim).
Mr. Barkin first met Amy Hall when he and Ron encountered her while, on a school field trip, they were searching for the Mount Middleton Snowbeast. Initially, Barkin was appreciative of Amy's treatment of him. But when she revealed herself as the creator of the monster (and a few others), Barkin immediately lost any interest in her, calling her “sick and wrong” (and unwittingly borrowing one of Ron's catchphrases in the process). She responded by turning him into a mutant monster.
When Shego showed up at Middleton High as a substitute teacher, Mr. Barkin was immediately smitten. Having been turned good by Electronique's modified Attitudinator, Shego was far more receptive to Steve's advances than she normally would have been. "Stevie" took Shego out on a date, which at Shego's request was a double-date with Kim and Ron; Barkin gave the young couple a quick out, though, and Shego and Barkin had a wonderful time. A second date at the skating rink never materialized, however, as by then Shego had been restored to her normal, evil self, although she hadn't formally broken off the relationship. After this, Barkin showed up at Drakken's lair to serenade Shego, with disastrous results that involved attack dogs and electric shocks.
- In "Tick-Tick-Tick" and "Royal Pain", his hair was blond, but starting with "Sink or Swim", it was colored brown for the remainder of the series.
- In "Tick-Tick-Tick" he was reading the Infiltration & Deception Manual while supervising detention.
- In the episode "Rewriting History", several flashbacks and an old photo of Steve Barkin's great-grandfather, Chief Barkin, are seen. Chief Barkin, who was Chief of the Middleton PD at the turn of the 20th century, appears to possess the same gruff, no-nonsense, inflexible personality as his descendant. However, these events were revealed to be a dream sequence so their canon is unknown.
- In the episode "Cap'n Drakken" it is revealed that his father is very similar to Steve, in both personality and his habit of constantly subbing for others.
- Throughout the series, he often calls his students by their last names (except of course Monique).
- In the episode downhill after Rufus and Mr. Barkin are un-fused and separated by the Genetic Zipper machine Rufus was wearing Barkin's clothes and Barkin was completely naked, but still with hair.