Harry was born in 1969 to a loving single mother and like Lloyd, an absolute idiot born. The exact fate of his father was never truly explained. Because of his idiocy and poor grasp of reality (As he truly believe his imaginary pirate friend Captain Rob was real well into his teens) Harry's mother knew it would be impossible for him to fit in socially with other children and home schooled him until he was a teenager. His mother decided to take a chance and allow Harry to attend regular High school where Harry would meet his life long friend and fellow idiot, Lloyd Christmas. In 1994, Harry accompanied his roommate and best friend Lloyd Christmas to Aspen to deliver a suitcase to Mary Swanson.
Dumb and Dumberer: When Harry Met Lloyd
Harry Dunne was born in a hospital in 1969, where he was about to come out of his mother's womb only to pop back in again. Eight years later, Eight year old Harry's imaginary friend, Captain Rob, falls down a well and has his mother call the police. The police then remind Harry that they can't keep trying to save his made up friend all the time. In 1986, Harry is now in his teens and he is about to start regular school after being homeschooled for many years.
Dumb and Dumber
In 1994, eight years after the events of Dumb and Dumberer: When Harry Met Lloyd, Harry is fired from his job as a dog groomer, because he took too long to get the dogs to the dog show and they were mess even after bathed and clipped. As soon he was home, Harry is informed by Lloyd that he, too, lost his job. He also learns that one of Lloyd's limousine passengers, Mary Swanson, left a mysterious briefcase behind unaware that she was turning in ransom money to get back her kidnapped husband Bobby. He mourns the death of his pet parakeet Petey, but thinks that Petey's "head fell off" from "old age," but, unknown to them, it was done by Joe Mentalino. Lloyd thinks that life is not cooperating with them and convinces him to leave their clueless lives and go to Mary's hometown: Aspen, Colorado, to meet up with Mary and return the briefcase to her.
For extra money for food along the way, Lloyd sold some baseball cards, a sack of marbles, and Petey's lifeless body to their next door neighbor, in which Harry becomes so astounded of, but Lloyd assures him he "took care of it."
They get stuck in several obstacles on the way to Aspen, Colorado. In Pennsyvania, they are targeted by a mean thugish 6' 4" trucker named Sea Bass, who blames an accident on Harry and soils his burger spitting in it. In revenge, Harry and Lloyd trick Sea Bass into paying their bill added in with theirs and along with other purchased items added in; and although escaping, Sea Bass vows revenge. Then, Lloyd needs to urinate really bad and Harry suggests to use beer bottles in their van to urinate in. Lloyd then relieves himself in about 5 bottles. While Lloyd takes care of it, they get pulled over by a snobbish police officer who accuses them of speeding and DUI. The officer then grabs a bottle and tries to drink what he believes is beer. Harry and Lloyd try to dissuade him, but he tells them to shut up just before taking a swig of the urine. Upon taking a swig of it, he groans and growls an order to "get the hell out of here!" and as they drive off, the officer vomits on the road.
Then, they pick up a man named Joe "Mental" Mentalino as a hitchhiker. They are unaware that Joe is one of Bobby Swanson's kidnappers who wants the briefcase to give to the primary kidnapper: Joe's life-long friend and boss Nicholas Andre. Mental is frequently annoyed by their stupidity and is forced to suffer annoyances of stuff like their tag wars ending with one of them arguing over whether or not "you can triple stamp a double stamp"; the most annoying sound in the world; and an annoying version of popular song '"Mockingbird"'.
At a restaurant, to drain his annoyance against Harry & Lloyd, he dares them to eat hot atomic peppers at the same time. In retaliation, Harry and Lloyd put peppers in his cheeseburger as he makes a phone call unaware that Mental has ulcer problems, and thus cannot eat acidic atomic peppers. Joe Mental decides to kill them with rat poison, but changes his mind when he learns that they have no idea on what is in the briefcase. When Mental has a reaction from the peppers, he falls backwards on the ground groaning from the agonizing pain in his stomach from his ulcer problem, he orders them to get his medicine. While Lloyd performs CPR and mouth-to-mouth recitation, Harry searches for the pills in Mental's jacket, but he ends up accidentally giving him the rat poison pills Mental was going to use. Mental sees the container, and then blames Harry for it with his final words calling him an "SOB" and making a gurgling sound and dies of the toxins. Harry and Lloyd flee, feeling guilty of killing Mental.
That night, Harry and Lloyd learn that they are now wanted by the police as fugitives for Mental's accidental death. As they stop at a gas station, Harry falls in love with a woman, who is also moving to Aspen, Colorado to get away from her boyfriend. Harry tries to ask her on a date, but sets himself on fire by accident. As he burns, he gets impatient with her getting off topic of her phone number, screaming "For God's sakes just gimme the damn number!!" Offended, the woman drives off refusing the offer and Harry charges into the bathroom. He bashes down the stall door, knocking out Seas Bass in the process, and proceeds to putting out his burning leg. After frantically putting out the fire, he sees Sea Bass lying on the floor after he knocked him out, and then Lloyd sucking his thumb in fear (Sea Bass found Lloyd and tried to sexually molest him and murder him in revenge).
That night, as they proceed on the road, Lloyd constantly reminds him of what happened and begs Harry to let it go, Harry promises not to mention another word of Lloyd being in the bathroom with a trucker with his pants down. After the next stop at a gas station, Lloyd ends up accidentally driving the wrong way to Lincoln, Nebraska, thus running them out of gas. This proves to be luck because if they reached the Colorado border, they would have been arrested for killing Mental due to officers tracking them down. The next day, Harry wakes up in Lincoln, Nebraska in fuel mileage drama. Nearly out of gas, they stop on a pullover site. Infuriated with Lloyd for his dimwittedness, Harry decides to walk back to Providence, Rhode Island. However, Lloyd realizes that the truck is not completely out of gas and drives to a nearby town trading it for a moped. He then catches up with Harry who grows happy with Lloyd for his idea and accompanies him on the moped all the way to Aspen, Colorado. After arriving in Aspen, they are unable to find Mary in the phonebook, due to her last name being forgotten.
That night, while camping in a blizzard, Harry, even with a campfire, cannot warm his fingers. When Lloyd reveals extra gloves on him, Harry gets enraged that his own friend did not give him extra gloves when it was clear that Harry was freezing. In return for it, Harry tries to throw the briefcase in the pond, but Lloyd stops him, and Harry tackles him to the picnic table and tries to strangle him, but after dropping the briefcase, it opens, and they see it has the money in it.
They decide to use the money to lodge up in a fancy hotel room in Aspen, a new car, among other posh items and track down their spendings with IOUs. They end up spending every penny of the ransom money, and eventually find Mary. Lloyd gets shy and asks Harry to ask Mary on a date for him. Harry agrees, but ends up asking Mary for a date for him and her. Harry lies to Lloyd that Mary will come for Lloyd the next day, but he really sneaks out of the hotel to attend his date with Mary. On his date, Harry shows his stupidity by licking a frozen flagpole getting his tongue stuck to it; putting a snowman's face in the wrong part of the snowman; among others, but Mary thinks it is intentional humor. Eventually, Lloyd learns that Harry arranged it for himself.
Angered with his friend for his treachery, Lloyd pretends to be normal as Harry prepares for another secret date with Mary. While Harry is sprucing himself up, Lloyd pours laxatives in Harry's tea and forces Harry to drink it in a so called toast for their friendship. The laxatives act up while Harry is on his way to Mary's, and even after meeting up with her before they're about to go on their date. The drink forces Harry to use the Swanson mansion toilet, and when he finishes, he finds that the toilet cannot flush. Stuck now with fixing the entire mess, Lloyd uses advantage of this pickle to pick up Mary and take her to the hotel to get her briefcase. Eventually, Harry figures out that Lloyd did it out of vengeance and decides to go to the hotel to reconcile and confess, but is picked up by the woman he shouted at in the Gas Station for an unmentioned reason.
When he arrives, he spots Lloyd and Mary handcuffed to the room bed. He finds himself being captured alongside his two buddies by Bobby's kidnapper, Nicholas Andre, who is enraged with Harry & Lloyd for spending the ransom money. While Nicholas Andre tries to book an escape to Europe, Harry and Lloyd angrily rant over who is in fault for ruining their friendship, causing Andre to order them to both shut up and decide who is shot first. Harry ultimately decides to take the bullets, but survives and retaliates against Nicholas with 5 missed shots from a pistol he somehow got. Then FBI agents rush into the room ambushing Nicholas and arresting him. The woman, Beth Jordan, turns out to be an FBI agent who is the leader of the kidnapping case; she used Harry to capture Nicholas and provided Harry the gun and bulletproof vest; but she shows some antagonism towards Harry when she says that the FBI did not care if he was fatally shot, or not but about capturing Nicholas off of it.
Eventually, Bobby is found and safely reunited with Mary. Harry and Lloyd do NOT get a heroes reward being that they put the cops and feds through so much trouble and aggravation. Now, with their trip useless and their bought possessions confiscated to pay their IOU debts, Harry and Lloyd decide to journey back to Providence, Rhode Island, with their moped breaking down in the process along the way. They unknowingly turn down an offer to become oil boys for girls going on a national bikini tour. They redirect them where a town may be for them to find oil boys. They are then seen continuing the journey back home, playing games of tags and quitsies.
Dumb and Dumber To
In 2014, 20 years after the events of Dumb and Dumber, Harry visits Lloyd every Wedensday in a Mental institution, One of those visits gives Harry the greatest shock of his life. He realizes that Lloyd had pranked him for over 20 years pretending that he was in a comatose state. Lloyd effectively wastes 20 years of both his and Harry's life.
Harry is an incredibly stupid man, although he showed signs that he was a little bit smarter than Lloyd on some things. He was also surprisingly charismatic, as Mary Swanson took quite a shine to him. He was prone to unintentional accidents, which usually brought disaster on himself and/or anyone in the vicinity. Harry also has no clue how to properly speak into a cell phone or intercom. He also tends to forget important events that have happened in his life. For example, when his mother died, he was passed on to a Chinese family. When they told him that he was adopted, he was quite shocked to hear that news. Harry's also completely ignorant of illegal activities happening right in front of his face. Like Lloyd, Harry also overestimates himself immensely. When he fantasized about him being a good father to Penny, in reality those parenting methods would have gotten him arrested.
"FOR GOD'S SAKES, JUST GIVE ME THE DAMN NUMBER!!!"
"I say we stay here, we hunt for jobs and we keep saving our money for the worm store. I don't know about you but I am getting sick and tired of running from creditors! I hate those guys! That's why I never went to college!"
"So you mean Pee Stain's the dad?"
"She gave me a bunch of crap about me not listening to her enough or something. I don't know, I wasn't really paying attention. But the thing that hurt the most, she was seeing another guy. I never did find out who."
"You know Lloyd, just when I think you couldn't possibly be any dumber, you go out and do something like this, AND TOTALLY REDEEM YOURSELF!!!"
"Your milk bubbles look nice, Jessica."
"Lloyd, please, shave my daughter and then I want you to bone her like a chicken cutlet. You hear me mister?"
"What are we doing sitting around yapping? Let's eat!"
"You knew I was crazy about Fraida Feltcher, but that didn't stop you did it?!"
"You're this close, but, there's a drawing board you should be getting back to. Next!"
"Check out the hotties at 12:00!"
"Good one, Captain Rob, he does look like a you-know-what."
"Say, kids, you wouldn't happen to have a cup of warm water, would you?"
"That was genius, Lloyd! Sheer genius! I mean, where'd you come up with a scam like that?"
Having been born in 1969, he is seen at age 8, and having the police "rescue" his imaginary friend, Captain Rob, out of a well. Years later, in 1986, as a teenager, he is about 17-years-old, by the time he meets Lloyd in High School in Dumb and Dumberer: When Harry Met Lloyd. In Dumb and Dumber, he would've been 25-years-old as the film takes place eight years after the events in the prequel. In Dumb and Dumber To, he would've been 45-years-old as the film takes place 20 years after the events of Dumb and Dumber. He's about a year older than Lloyd, who was supposedly born in 1970.