Tim Templeton is the main deuteragonist of the film The Boss Baby.
He was voiced Miles Christopher Bakshi as a child, while as an adult, who also narrates, he was voiced Tobey Maguire, who was well known for playing Peter Parker/Spider-Man and Nick Carraway in The Great Gatsby.
Timothy "Tim" Templeton is the firstborn son to Ted and Janice Templeton. He is seven years old and is shown to be quite the imaginative and energetic boy. One morning he wakes up to the sound of the alarm clock and looks out the window to see a taxi arriving. Out of the taxi, appears Boss Baby dressed in a suit. A shocked Tim runs downstairs to confront his parents only to see them introduce him to his new younger brother.
Tim quickly grows jealous of his younger brother as he takes up all the time and attention of his parents. Tim tries to tell his parents that the baby is not normal and is manipulating them into doing what he wants. This is seen true when his parents leave the room and Boss Baby begins to give a sour look to Tim and begin to fight. His parents, of course, side with the baby when Tim blames him as they just see the baby acting as a baby does.
During the nights, Tim is unable to sleep because of Boss Baby's relentless crying and his parents buzzing around the house trying to calm the young baby. He grows to resent his new younger brother.
One night, Tim expects his parents to tuck him in, hug him, tell him stories and sing him in songs in order for him to sleep, a special tradition that occurred before the arrival of Boss Baby but his parents have fallen asleep from exhaustion in the living room and when Tim hears a phone ring and realizes it isn't the home phone from the living phone, he follows the ringing to his younger brother's quarters. There, he finds out that his suspicions are correct and that Boss Baby can talk and has been manipulating Tim's parents. Tim reveals himself and calls Boss Baby out resulting in Boss Baby trying to cover it up with baby speak but failing. Eventually Boss Baby reveals himself to Tim and explains what he's doing, steal Tim's parents' time and attention away from him. Tim threatens the baby with exposure of his ability to talk but Boss Baby knows they won't believe Tim.
The following day, Tim figures out that the only way for his parents to believe him is if he manages to find proof of the baby's ability to speak by recording him. He prepares technology as a hearing device, a mask, tape recorder, etc to get evidence. He rushes through the hallway like a ninja and trips on a toy in the staircase leading to him tumbling downstairs only to be discovered by a group of babies led by Boss Baby. Jimbo is about to drool in his mouth when Tim's parents walk into the room and the babies resume acting like ordinary babies. After the parents leave, the babies decide to begin their meeting. Tim stays from a distance to record their voices and plans with his tape recorder but this plan is stopped as Boss Baby orders Jimbo to create interference with his rattle.
During this time, Tim manages to listen in on the problems of Boss Baby and his associates. He finds out about BabyCo's problem of puppies stealing the love away from babies. This would lead to parents having less babies and bankrupting the company. He learns that PuppyCo is to reveal a new breed of puppy that is said to put all of baby-kind in jeopardy. During this meeting, the parents once again walk in and begin to take pictures of the babies in their "play meeting". After they leave, Boss Baby utters how embarrassing it was to have to behave like a baby, Tim manages to record this one line and has the proof to show this to his parents. The babies quickly grew wind of this plan and attempted to confiscate the tape to not reveal their identity. The babies begin to chase Tim. Tim is about to enter the room where his parents are before the babies arrive to detain him and steal the recording. After a whole chase scene, which has the tape flying from the babies and Tim, Tim manages to escape with the tape to the second floor but Boss Baby follows him. A chase continues until Tim opens the door to an out-of-control Boss Baby stuck inside a toy who rolls out of the house. Tim, feeling victorious, heads to show his parents the proof in the house's office only to find out that Boss Baby is the one in the office. Tim is flabbergasted as he saw Boss Baby leave the house out-of-control.
Boss Baby and Tim continue to fight and Tim is about to toss Boss Baby out of the window using a slingshot until caught by their parents. Boss Baby begins to cry and the parents angrily ask Tim what he's doing, he replies with "Nothing." and instead of Boss Baby, accidentally tosses the tape outside the window and onto the street where it gets run over by a passing car. Janice Templeton is furious at Tim and decides to ground him for "three eternities". Tim is next seen imaging himself inside a prison cell counting away his days until he's talked to by his wizard alarm clock. Eventually Boss Baby enters Tim's "prison cell" or room to try and comfort the boy as he feels bad for what he did. Boss Baby offers Tim if he wants to see what BabyCo is and what their plan is. Tim agrees and both of them use pacifiers to transform themselves into holograms and see the BabyCo building. There, Tim asks if this is where babies come from. Boss Baby confirms this and Tim tells Boss Baby what his parents told him about where babies come from only to see Boss Baby wince in disgust.
Boss Baby explains what keeps the babies young forever, which is their milk formula. He shows him the problem that puppies are stealing the love of adults from babies which has them is a state of distress. Boss Baby then shows the Hall of Popular and Most Acknowledged Boss Babies. Here, Boss Baby shows Tim someone he admires, Super Colossal Big Fat Boss Baby. After Boss Baby witnesses his boss ask about Boss Baby and his progress of finding out what the new type of puppy PuppyCo is planning to release and if he doesn't he'd be fired. Tim is forced out of this hologram state and back to the real world where he has to deal with a stressing-out Boss Baby. Tim agrees to help Boss Baby in order to remove him from his household.
Boss Baby and Tim check their parents' files when they are asleep in the living room. Eventually they find out that they're going to reveal this new puppy in Las Vegas. They also find out that Take Your Son to Work Day is approaching and that with that, they can enter PuppyCo and extract the information they need but since Tim is grounded, they are unsure if they will be able to go. They agree that the only way for Tim to be allowed to go is if he proves that the brothers have grown to love each other which will lead to the parents ungrounding Tim though they both reluctantly agree. This leads to Tim trying to feed Boss Baby, Tim trying to put on a sailor suit on Boss Baby for a photo shoot and Tim reading Hansel & Gretel to Boss Baby. The parents see this and are happy about this.
The next day, Tim is woken up by his parents and is surprised and happy to hear that he's ungrounded and that his parents plan to take him on Take Your Son to Work Day. Tim asks if Boss Baby can go too and they agree. Eventually the family arrive at PuppyCo and see all the puppy-based attractions and rides. Tim's parents offer Tim the opportunity to spend a day alone with just them since they see that they haven't been spending too much time with Tim. Tim looks as if he is going to accept this offer but refuses in order to continue Boss Baby and his mission to find out the new puppy. They understand but instruct them to stay in the Puppy Room. They find out a large door with a guard that doesn't allow children or unauthorized personnel. The two brothers organize a plan to sneak the baby in using a puppy suit, pretending to be a puppy through the Puppy Door. This leads to crazy hi-jinx but the two manage to slither inside the restricted space.
The two stumble upon a room with many files and folders. Tim and Boss Baby arrive to see a confidential file on a pedestal. Tim stops Boss Baby from simply taking it though saying that he's seen this before and that they have to replace the current file with another file so they don't trigger the trap. They succeed but Boss Baby becomes too excited and accidentally drools on the replacement file triggering the trap which leads to large domino effect which ends with the two captured. The file they took is shown to be a decoy and they see a man in a puppy suit reveal himself. Then later, Francis E. Francis confronts the baby and Tim. Baby Boss asks why Francis Francis is doing what he's doing. Francis E. Francis reveals his identity and story to the two. Francis E. Francis is actually Boss Baby's idol, Super Colossal Big Fat Boss Baby who had grown up after he was fired from BabyCo because he was lactose intolerant so he couldn't drink the eternal youth formula leading to him aging and him being less popular among the babies leading to eventual replacement with Boss Baby's current boss. Francis E. Francis was sent to a farmer's family where he grew up with only revenge in his mind. Eventually Francis reveals that the puppy he plans to reveal is a puppy that never ages by using the key component of the babies' eternal youth formula which is unknowingly brought to Francis via Boss Baby.
Francis then tells him of his plans to take Ted and Janice Templeton to Las Vegas while leaving Tim and Boss Baby under Eugene's care, who will be dressed as a nanny. Eventually, they are released and Francis's plans continue without interruption as Tim and Boss Baby are trapped inside their own home under the supervision of Eugene. Tim comes up with a plan to make Boss Baby appear sick and vomit but the vomit is artificial and blasted through a vacuum cleaner. Eugene is disgusted by this ordeal and retreats to puke in the toilet. Boss Baby and Tim trap Eugene's head in the toilet and proceed to run away using Tim's bike. Eugene continues to follow the two even with a toilet on their head. The two and Eugene engage in a chase heading towards the airport to stop their parents from leaving to Las Vegas with their parents. Boss Baby calls upon the aid of his associates. The triplets, Jimbo and Stacey succeed in stalling Eugene but are unable to stop him. Eventually Tim's bike loses its training wheels which causes Tim to panic as Tim is unable to ride a bike without training wheels. Boss Baby helps Tim though and he becomes able to ride his bike without the wheels. They manage to lose Eugene. The two arrive at the airport and are very close to their parents but Boss Baby begins reverting to a normal baby as his formula was stolen by Francis. Tim is forced to return to retrieve Boss Baby but that causes them to waste time and Francis manages to quickly escort the parents into the plane before Tim and Boss Baby are able to interact with them.
This causes Tim and Boss Baby to go into a fight as they believe that they have failed and that there's no hope. Eventually Boss Baby leaves in a rage leaving Tim to be sad. Tim stays crouched near the window to the airstrip for hours until he receives a call from Boss Baby who reconcile and decide that they can still make it to Las Vegas via a plane by the Elvis Convention. They steal an Elvis outfit from a man in the bathroom and make their onto the plane where they find themselves in first class where Tim teaches Boss Baby how to use his imagination. They arrive in Las Vegas and decide to hitch a ride with some girls to the Las Vegas Convention Center. But it is revealed that Eugene managed to follow them dressed himself as an Elvis impostor. They make their way to the reveal of the eternally young puppy. Everyone in the convention, including Eugene, is awe-struck at how adorable the puppy is. Boss Baby protects Tim from seeing it. Tim eventually grabs the attention of his parents, prompting them to ask why the kids are not home. Francis, in a panic, throws the parents inside the reveal box. Tim and Boss Baby follow a fleeing Francis to a room with a large rocket full of eternally young puppies that is to be sent to deliver puppies all over the world.
Tim and Boss Baby manage to escape Eugene again and confront Francis. Francis tries to bring Tim to his side, telling him that they were both neglected and had their love stolen away from babies. Tim stays on Boss Baby's side. The two are eventually defeated by Eugene and are left hanging on a railing over a pot of anti-aging formula. Fortunately, the two use their imagination to imagine a pirate battle and manage to overpower Francis and instead toss him into the anti-aging formula. They're about to stop the rocket from flying off but Tim hears his parents' cry for help and Tim goes to help them. The hatch of the rocket opens and Boss Baby is on it right before it takes off. Boss Baby, unfortunately, reverts back to a normal baby and Tim needs to lower him from there before it takes off. Tim sings one of his parents' songs and he calms the crying baby down and manages to lower him from the hatch. He gives Boss Baby a drop of the pure anti-aging formula transforming back to normal. Francis, reverted back to a baby, surfaces from the formula intent on revenge.
He is stopped by Eugene who gives him a pacifier and leaves to raise Francis the right way this time. Tim and Boss Baby return to free their parents and their mission is complete. Boss Baby bids farewell to his associates and Tim. But Tim and Boss Baby had grown to love each other and begin to miss each other. Tim's parents' memories of Boss Baby are wiped by the BabyCo workers and life resumes as normal. But one day, Tim sends a letter to Boss Baby that has a callback to a conversation they had near the beginning of the film. An ecstatic Boss Baby leaves his office running, breaks the BabyCo system by messing with the love pie chart and he rips off all his clothes and heads to the baby conveyor belt from the first seat to return as the Templetons' youngest child. The scene with Boss Baby arriving in a taxi is repeated but this time when Tim is introduced to Boss Baby, he embraces the baby and they grow up together and have a happy ending.
In the end, we skip to Tim telling his daughter the story. Tim's daugther wonders about if that is exactly the way it happens but he asks her to ask her uncle, which is a grown-up Boss Baby as the three refer to Tim's daughter's newest sibling. A daughter, who comes dressed in a suit much like Boss Baby did in the beginning of the movie.