The show's protagonist and youngest member of the Test family. Johnny creates many of the show's plots through his willingness to abuse his sister's inventions or cut some corner in life. His best friend is Dukey, his (talking) dog. Occasionally Johnny fights crime using superpowers gained from his sisters under the name Johnny X.
Aesop Amnesia: Johnny learns lessons. He just never remembers those lessons.
Annoying Younger Sibling: And apparently, he's holding back. He once got his sisters to agree to do something by threatening to somehow be 100 times more annoying...it worked!
Blackmail: In the early seasons, around how Johnny convinces his sisters for a favor, the blackmail usually being 'unapproved' experiments.
Blah Blah Blah: What Johnny always says whenever Susan and Mary try to tell him how their invention works or warn him about overusing it.
Book Dumb: Clever and manipulative, but a poor academic performer.
Brilliant, but Lazy: He only SEEMS stupid, he's just too dang lazy to apply it to school or much else. However, if its something that has to be done or he really wants to do, he can come up with plans even his sisters find downright amazing.
Can't Get Away with Nuthin' : If Johnny uses some advantage for personal benefit, it will almost certainly backfire on him by the end of the episode. In a few instances, he has to use the advantage for the greater good, costing him his benefit.
Good example is where he obtained x-ray vision to win at a gameshow, the prize being enough money to be set for life. Before he can actually select the suitcase and get the money, Dukey convinces to go and save the library from being taken by the mole people.
Spoiled Brat: Subverted. While he has to resort to Blackmail or begging to get what he wants from his sisters, they more or less often experiment on him as frequently and could be seen as a form of 'payment.'
Johnny's talking dog who was genetically enhanced by Susan and Mary some time before the series. Dukey's main job is to act as Johnny's voice of reason even if he's prone to being ignored. That said, he's more than capable of doing the wrong thing himself if properly motivated (such as with steaks). On more than one occasion he acts as a crimefighter alongside Johnny under the monikers Super Pooch, X Pooch or Super Dukey, though after the earliest incidents he expresses a dislike for doing so.
The letter in this case is a holdover from when his alter ego was called "Super Dukey". The writers have since flip-flopped on exactly what his superhero handle is between "Super Dukey", "Super Pooch" and "X Pooch".
Martial Pacifist: Susan and Mary included the DNA of Kung Fu masters in his genetic code, making him a skilled martial artist...however, he doesn't like using it and more often would just prefer to stay at home and goof off than fight supervillains. He also refuses to teach it to Johnny since he knows Johnny doesn't have enough self control not to use it.
Master ofPaper-Thin Disguise: Works due to most people in their world being stupid. He normally just says he's a 'kid with a rare hair disorder' and they believe him. He also sometimes wears a t-shirt that says Not A Dog.
Morality Pet: Played with in the fact that although he tried to convince Johnny something is wrong (or right) to do, he often fails at changing Johnny's mind unless it has to do with his family. Also tries to convince the Sisters that treating Johnny like a guinea pig is wrong. Fails in that as well.
The Other Darrin: In Season Five, Louis Chirillo has been replaced with Trevor Devall. And it is EXTREMELY noticeable, with the entire voice pitch changed and Trevor struggling to keep the same inflections with obvious throat pain (going by the rough, scratchy noises). And for all his effort he just ends up sounding like Hugh Test.
Johnny's older twin sisters who attend the Mega Institute of Technology. Both are geniuses capable of devising whatever machine the plot demands and most episodes relate at least partially to one of their experiments. Both Susan and Mary have a crush on local boy Gil that can work against them. Susan is also the object of affection of resident villain Bling-Bling Boy. Both sisters look identical except for their fashion choices (Susan wears squared glasses, a skirt and knee socks and has straight hair; Mary has curved lenses, wears jeans and has curled hair).
Balloon Belly: Not as often as Johnny or Dukey, but they will gorge themselves on occasion. One time they fattened themselves up with candy, and another they got bloated from eating too much ice cream.
Love Makes You Crazy: Their attempts to get Gil to notice them always backfires or screws up. Not to mention fighting one another over who will marry Gil, ending up with them becoming a couple of messes, which derives Gil's attention to Johnny.
Nice Job Breaking It, Hero: They end up causing the disaster of the week as often as Johnny, and more often than not end up needing Johnny's help to fix it.
Not So Different: Susan and Mary's ploys to get Gil's attention can be eerily similar to Bling Bling Boy's attempts to get Susan. For example, they both turned themselves into babies to be sat by their crushes. Interestingly enough, this has not been pointed out as of yet.
Red Oni, Blue Oni: It's subtle but it's there. Susan is the red: more rational minded, always tries to see if there's logical explanation for everything and can be rather stubborn. Mary is the blue, willing to believe more in the unnatural and is usually the voice of reason between the pair. There's also a dash of Tomboy and Girly Girl with the way of dress (Susan wearing a skirt and Mary Janes while Mary wears jeans and sneakers.)
Captain Ersatz: Though both shows came out around the same time, Gil is a local, well meaning blonde kid who is the object of the protagonist's older sister(s) affection, drawing many easy parallels to Jeremy on Phineas and Ferb. The two started to deviate later when they both started being less Flat Character sorts.
Catch Phrase: "Hey, Johnny!", or "Tell Johnny I said hi!" whenever Johnny's not around.
Murder the Hypotenuse: Bling-Bling plotted to get rid of Gil so Susan would focus her attention on Bling-Bling Boy.
Not-So-Harmless Villain: While his attacks normally revolve around getting Susan to be his girlfriend, when he snaps on occasion, he is extremely dangerous. Never underestimate a genius with infinite funds and a huge army at his disposal.
Corrupt Corporate Executive: He's the head of a toy company named after him, but devotes all his time to finding ways to get rid of kids.
Cut Lex Luthor a Check: Averted, sorta. His board of directors asked him if they'd go out of business if his plan succeeded. Turns out he'd already thought of that and programmed his robots to offer to 'babysit' the kids for free to keep their parents happy. Still, he's a brilliant enough man that his smarts could be better spent elsewhere.
Devil in Plain Sight: His company is still afloat despite him being obviously psychotic and his company producing extremely dangerous toys with the intent to maim or 'get rid of' kids. Handwaved in that his legal team is apparently extremely good.