Baljeet has been a part of the series since its pilot, filling a role in the friend circle of the show's alleged protagonists, the Phineas and Ferb of the title. However, the form of a 7-year-old human male is actually a disguise created by Baljeet in order to interact with the people of Earth. In reality, he is a highly-powerful cosmic entity capable of traveling through all realms and dimensions of the Phineas and Ferb multiverse. Though he is far from the strongest being in the multiverse, Baljeet's universal energy makes him immensely more powerful than any forces in the world where he currently resides, home to the series. This allows him to control the world around him and also explains the ability of the boys to create all their physically-impossible inventions. Though the viewer of the show watched Phineas and Ferb create all their machines, they are only being controlled by Baljeet, who exercises his psychokinetic abilities to give them both the ideas and skills they need to defy all physical laws of their world. But why would Baljeet want to help the boys accomplish this? What is Baljeet's plan on Phineas and Ferb's Earth (henceforth referred to as F-Earth), and how did he reach it? This can be explained with the information found in One Good Scare Ought to Do It, the ninth episode of the first season of the series. Most important to uncovering Baljeet's identity, however, are the events that transpire in the last moments of the episode.
Since this episode occurs very early on in the running of the series, we can assume it is during Baljeet's earliest experiences on F-Earth, more specifically on the ninth day after his arrival. Knowing Baljeet's powers, we can also infer that he travels freely through many dimensions and realms at will, and happened to find F-Earth in his travels. The exact reason for his stopping in this location is yet unknown; however, some speculate that he took interest in the world and decided to explore it after noticing the diversity of life there; the coexistence of triangular-headed people like Phineas, rectangular-headed people like Ferb, and normal-looking people like their parents may have fascinated him. Having landed on F-Earth, Baljeet decided to assume the form of a human there in order to gather more information about them, which brings us to the time of Season One, Episode Nine, the ninth day of Baljeet's reconnaissance mission among the neighborhood kids (Buford, Isabella, Phineas, and Ferb). Though Baljeet could have just as easily disguised himself as a human adult and befriended other such humans, like the parents of the children, his disguise may be weak and quickly-formed; this means that any close interaction with more intelligent humans may pose the threat of his true identity being uncovered. This could be catastrophic, as humans of a low-level planet such as F-Earth would lack the interdimensional perception of Baljeet and perceiving his true form could cause their minds to collapse. Therefore, we know that, at the time of S1E9, Baljeet had spent nine days on F-Earth under the disguise of a 7-year-old boy in order to learn more about the planet without being discovered.
In this episode, as in every other episode, Baljeet helped the boys to create an impossible machine - this time a massive haunted house - in order to impress them with magic and gain their trust. However, if one of Baljeet's creations were to be discovered by a highly-intelligent life-form, like an adult human, it could cause them to realize his true non-human status. Therefore, Baljeet must destroy each of his wonders before the boys' mother, Linda Flynn, arrives to see it. The viewers of the show are able to see this destruction take place, but may not understand how it happens. It would seem, to viewers, that each creation is destroyed in the aftermath of a mission conducted by the boys' pet platypus, who lives his own secret life as a government agent. However, much like the existence of the boys' machines, the ability of a platypus to conduct secret missions is impossible by all natural laws. Therefore, the platypus is only able to carry out its missions under the control of one being: Baljeet. This means that, in each episode, Baljeet first helps the kids to create their wonderful machine in order to gain influence over them with his magic. Then, he must simultaneously manipulate the events involving the platypus and the aforementioned machine to ensure that, with ever-convenient timing, his work is destroyed and nobody ever learns anything about his identity. Clearly, this process is strenuous even on the extradimensional abilities of Baljeet; therefore, the difficulty of enacting his plans makes his downfall in S1E9 all the more understandable.
But just what happened to Baljeet in One Good Scare Ought to Do It? In the final moments of the episode, the platypus is seen narrowly dodging a falling machine designed to completely destroy whatever it touches; the machine then falls on the haunted house, wiping all traces of it from existence. This, as explained above, is all a part of Baljeet's plan and is under his control. However, rather than go home as he does in every other episode, Baljeet does not leave the Flynn/Fletcher family's backyard by the end of the episode. When seen by members of the family (more specifically Linda and Candace Flynn), Baljeet explains that he forgot his satchel, which he then holds up to show them. However, the problem lies in the fact that, though Baljeet did lose his satchel, he was never able to recover it. In reality, the satchel of which he speaks was destroyed along with the haunted house, and Baljeet is not powerful enough to reverse time long enough to recover it. When he appears to hold up the missing satchel, he is actually creating a holographic projection of the bag so the F-Earth occupants will not become suspicious about why he is still in the yard. When the episode ends, Baljeet is not shown walking away from the yard; this is because he is still there, presumably in shock over having lost his satchel forever.
The importance of the satchel to Baljeet is actually fairly simple. Though Baljeet is extremely powerful, his strength relative to the size of the whole Phineas and Ferb multiverse is actually quite average; this means that he is not yet powerful enough to traverse all the realms on his own energy. Baljeet's satchel is what helps him to navigate through space-time like he did to reach F-Earth at the beginning of the series. Without the machine inside his satchel, Baljeet is now stuck on F-Earth and cannot return to his home in the Baljeet realm. Because of this, Baljeet's actions for the rest of the series revolve around reforging his satchel and escaping from the realm where the show takes place. In order to regain his satchel, Baljeet's only option is to train himself on F-Earth until his skills are refined enough to forge a new one. The difficulty in this is that, being a simple planet and weak in magic, F-Earth lacks the materials out of which Baljeet's first machine was made. This means that, though Baljeet understands how to build a new timespace transportation satchel, he will have to reach immense power in order to acquire a new one; however, Baljeet believes that enough training will allow him to harness the very forces that bind the multiverse together, extending his influence outside of his current realm and allowing him to summon the parts he needs.
Therefore, the entire premise of Phineas and Ferb is as follows: Baljeet is a powerful extradimensional nomad who decided to research F-Earth in his travels. He lands on F-Earth, assuming the form of a 7-year-old boy, and creates great wonders for neighborhood children, beings who are not powerful enough to see through his disguise, in order to gain their trust. However, his attempts to create and destroy each wonder in a day caused him to lose focus on the ninth day, resulting in the destruction of his satchel and stranding him on F-Earth with the children. Now, he must continue to create wonders, progressively increasing their complexity, in order to train his skills. Baljeet hopes that, with enough practice and training, he will become powerful enough to reforge his satchel and return home.
However, there are more complex factors at play in Baljeet's quest. To be precise, two other characters of the show actually did not exist until Baljeet landed in F-Earth at the beginning of the Phineas and Ferb series: these are Buford van Stomm, another friend of the children, and Candace Flynn, the older sister to Phineas and Ferb. Before the start of the series, which is approximately when Baljeet landed on F-Earth, these people did not exist and were unknown by any of the realm's occupants. This is because they, like Baljeet, are not human inhabitants of the realm. Instead, they are also powerful entities from distant realms of the P&F multiverse.
The first to mention is Buford. Though "Buford" assumes the form of another child like Baljeet, his true purpose on F-Earth is to keep Baljeet's power in check and limit his influence of the planet. This is because Buford is actually a much more powerful cosmic agent who was created when Baljeet began to interfere with realms outside his own, and exists to enforce the balance of the multiverse. He has been following Baljeet throughout his travels, monitoring his behavior and guarding weaker realms from his magic. What appears to the viewer as petty harassment of Baljeet is actually an assertion of dominance, as Buford subtly threatens to destroy Baljeet with his superior magic if Baljeet oversteps on F-Earth.This is why this being assumed the form of the "bully" of the group, and why Baljeet lives in fear of his violent temper throughout the series.
Another force of the universe working against Baljeet takes the form of Candace Flynn, the older sister of the brothers Phineas and Ferb. In each episode, the entity assuming the form of Candace desperately tries to show the work of the children to Linda Flynn, a normal human citizen of F-Earth with close ties to the kids. However, her efforts are always in vain, as Baljeet succeeds (though often narrowly) in destroying his creations before they are discovered. Though the adults of F-Earth would surely discover Baljeet's true power if they found any example of his magic at work, the group of children simply suspend their disbelief and see Baljeet as little more than a highly-intelligent human boy. However, if Candace were a normal teenage human of F-Earth, she would likely be able to realize Baljeet's identity; and if a human were to understand this, Baljeet would be destroyed for having revealed the forces of another realm to F-Earth inhabitants. The reason that Candace is not surprised by the creations of the children is because she did not come from F-Earth. Instead, Candace is a being of pure evil, spawned from the dark energies of a realm near F-Earth. Seeing Baljeet's interference in F-Earth, this dark wraith decided to use its power to attempt to cause the downfall of Baljeet by revealing him to the creatures of the world he found. This is why "Candace" seeks to show her mother every one of "the boys'" creations; she believes that this will result in the demise of Baljeet and create a disturbance in the multiverse. However, her efforts are never successful, as her power level is much lower than Baljeet's and he always foresees her plans and stays ahead of them.
This information is the true story behind Phineas and Ferb. The two lovable boys of the title are only moved into a position of attention by Baljeet, who is behind every single event in the series. He uses them, as well as the other array of characters on the show, in order to defer attention from himself as he attempts to raise his power level. Though it seems as though the children only have 104 days until their Summer vacation ends, the real significance of the span of time is that Baljeet only has 104 days to reforge his lost satchel before his distance from home strands him on F-Earth for all eternity. As he works to refine his skills to escape from the low-level world of Phineas and Ferb, he must race against the plans of "Candace", who wants to see him destroyed and feed off the residual energy caused by the resulting multiversal disturbance. He must also confine his wonders to the Flynn/Fletcher family's backyard or risk punishment from "Buford", another being who seeks to limit his interference in realms with magic weaker than his own. With many obstacles in his way, Baljeet's efforts to save himself after losing his satchel in the ninth episode of the series actually comprise the entire plot of the series. However, in order to keep the show understandable for young audiences, the true themes and inner workings of Phineas and Ferb are never explicitly shown or mentioned, except for the brief reveal about the satchel in S1E9. Instead, the show is viewed with a skewed lens - the platypus appears to live its own secret life, the boys appear to be the geniuses behind the machines, Baljeet appears to be an ordinary (albeit hardworking) student, and coincidence seems to drive the "clean slate" principle by which every episode seems to end in the same position as its beginning - in order to keep Baljeet, the true driving force of the series, "behind the scenes" for the young target audience. However, now the truth is revealed. Now we understand the secrets of Baljeet and his incomprehensible cosmic power. Now mankind can truly understand what Jeff Marsh has been hiding for ten years in Phineas and Ferb.