Lawrence "Larry" Quinn (Alec Baldwin) is the main antagonist of the 2003 live-action film adaptation of The Cat in the Hat. He is the unemployed next-door neighbor of the Waldens' and Joan's ex-boyfriend. He was determined to marry Joan so he could live off her and send Conrad away to military school. He prefers to be called Lawrence but he’s called Larry by Conrad.
A nasty and unemployed slob with dentures, Larry has very poor manners, such as belching in public, and lives in financial debt because he‘s unable to pay off his debts. He is the Waldens' next door neighbor and in a relationship with Joan, but he is dating her for real because he wants to marry her for her wealth and cares little for Joan's feelings. Larry is obviously allergic to cats as well, as shown in the film when he sneezes in the presence of the Cat in the Hat. He also dislikes being called Larry (as an insult by Conrad).
He dislikes Conrad as he thinks of him as a foolish kid and a rule-breaker who will never amount to anything in life. He’s also very insensitive; at first, he suggested to send Conrad into military school to straighten up his discourteous behavior, but it turns out that he only wants to do it to get rid of him. It's possible that he also dislikes Sally and dog Nevins (along with other children and animals), calling her a "suck up" for her sycophant faithfulness to her mother and views the latter an insignificant animal, and even attempting to catch them in trouble with Joan as well. This shows he wants to dispense Joan with her kids so he can maintain control of her and be able to leech off her money.
Larry found the family's dog next door in his yard, thanks to Conrad's reckless stunts, and returned him. Joan and Sally are fond of him, Conrad is not, knowing he's not who he appears and calls him Larry. The feeling is mutual; as Larry believes Conrad should be sent to military school as a solution to his rowdy behavior. Joan is not sure it's right for her son. Then Larry shows his manipulative side, telling her more about the military school, but Joan doesn't respond to the offer when the phone rings. He and Conrad share hostile words, the former explaining his plans for the boy's mother. After that, Larry departs, stating he has to depart for a meeting. As Joan leaves as well to return to her office soon enough, however, he stiffly exits his car and returns to his own house, all of which is observed by Conrad.
Later on, Larry returns to see the kids jumping on the couch. After calling Sally a "suck-up" who is just as bad as her older brother, he reveals his nasty side by stealing some beer and bread, and he impolitely belches in the kids' faces and compliments to the sandwich he's eating. The Cat in the Hat, dangling above Larry from the ceiling, scratches himself and causes the man's allergy to cat dander to stir. Sneezing uncontrollably, he urgently flees.
In his home, Larry shows his true colors: a work-shy, heavy, unemployed slob. He is sitting around his dirty home watching TV and lives in financial ruin from his many unpaid debts. Too work-shy to find himself a job, he plans to marry Joan so he can mooch off her and pay off his debts. As repo men show up and repossess Larry's TV, much to his dismay, after he fails to bribe them with an expired credit card, he sees Nevins on the loose again. He informs Joan and captures the dog, intending to use this to get Conrad in trouble and have his mother send him away.
As Larry and the kidnapped Nevins drive away into town, he gloats about sending Conrad away, only for Nevins to whiz on the taco he was eating. The kids and the Cat follow close behind him and take Nevins back, resulting in a chase around town. In a deleted scene, Larry sees the repo men take the TV into a TV shop called Safari Sam's. The Cat and the kids trick Larry into giving Nevins back, then he chases them into a secret dance club. But as he starts losing them in a club, he rushes to get Joan and convinces her to head home to prove the children's mischief. Upset when pulled over by Thing 1 and Thing 2, Larry impatiently rushes to the house after seeing his car in use by the trio. He corners Conrad and Sally, but he gets the sneezes again and the Cat taps him on the shoulder, frightening him, causing him to stumble backwards and fall off a cliff, screaming "Judas Priest!", revealing "the Mother of all Messes" coming from the Cat's magic crate. Then, all of a sudden, he plummets into a purple stream.
After everything was restored, Larry, who survived his fall, now covered in purple goo, is flushed from the house. After a period of time, he shows up at the Walden household and tries to persuade Joan about the events that happened, but she doesn't believe his story before claiming that although Conrad is ill-behaved, he‘s still a good kid and trusts him, and demands him to leave their home. Then Larry breaks down in tears and tries to propose Joan, only to repulse her by sneezing into his hands (exposing his true nature) and he is heard sobbing inappropriately from outside after Sally and Joan shut the door on him.
It's unknown what happened to Larry afterwards (though in a deleted scene, as Larry sadly leaves the Waldens' house, angered that he lost his chance of marrying Joan for her money and sending Conrad away to military school, and he spots Nevins licking a splotch of purple goo and tries to kick him out of rage, but the purple goo Nevins was licking transformed him into a bigger dog and fights back, ripping Larry's pants off and being chased away by the mad dog while the repo men are towing Larry's car away). It’s also likely presumed that Larry will eventually be homeless, unless he finds employment.