In the film, Old Man Marley was Kevin's neighbor. He was called "the South Bend Shovel Slayer", and was said to have murdered his family and half of the people on the block with a snow shovel back in 1958 and has been hiding out in this neighborhood ever since by Kevin's older brother Buzz. The cops didn't arrest him because of a lack of evidence to convict, he was also said to have kept his victims in his garbage can full of salt, and that the salt was supposed to have turned the dead bodies into mummies.
When Kevin meets Marley outside his house while Kevin is saying he is not afraid anymore, he screams, turns and runs back inside his house, afraid.
Later, Kevin goes to the drug store, gets a toothbrush and asks the clerk about whether or not it was approved by the American Dental Association. Marley then comes in while Kevin is checking his pockets to see if he had brought enough cash to buy the toothbrush. Kevin then looks up, sees Marley and backs away a little before running off while also accidentally taking the toothbrush he was holding with him, because he didn't have time to buy the toothbrush.
Later when Kevin goes to church, he meets up with Marley again, and learns that he's actually a nice guy, a Christian and a father, and that he didn't murder his family like Buzz claimed, but rather had an argument with them - more particularly, his son. Marley tells Kevin that he came to hear his granddaughter sing, and that he can't come and hear her tonight. When Kevin thought that meant he had plans, Marley corrected him, saying that he wasn't welcome - not at the church (as he believes one is always welcome at church), but with his son.
According to Marley, years back, before Kevin and his family moved into the neighborhood, he and his son got into an argument for an unknown reason as a result of losing their tempers, and told each other they didn't care to see each other anymore, causing them to become estranged from each other having not spoken to each other ever since. Kevin asks Marley to call his son, and Marley says that he's afraid to because he thinks that his son won't talk to him. Kevin tells Marley that he used to be afraid of his basement until he turned on the lights, and that Marley should call his son, and whether or not his son talks to him, Marley will know and he won't be afraid. Kevin tells Marley that he should also do it for his granddaughter, who probably misses him and the presents. Marley tells Kevin that he sent his granddaughter a check for Christmas, and Kevin tells him he wished his grandparents did that, but they usually send him clothes.
Later when the Wet Bandits trapped Kevin at the Murphys' house Marley sneaks in, and saves him by knocking the burglars out with his shovel and takes Kevin back home. At the end of the movie, Kevin walks over to the window, and sees that Marley has taken his advice and reunited with his son, daughter-in-law and granddaughter. Marley sees Kevin and waves to him, grinning, as a sign of thanking him formaking it possible for him. Kevin waves back, also smiling. Then Marley turns and goes to his house with his family to celebrate Christmas.
- You can say hello when you see me. You don't have to be afraid.
- There's a lot of things going around about me, but none of it's true.
- (About the church) This is the place to be if you're feeling bad about yourself.
- How you feel about your family is a complicated thing.
- Deep down, you'll always love them. But you can forget that you love them, and you can hurt them and they can hurt you, and that's not just because you're young.
- You're always welcome at church.
- You can be a little old for a lot of things, but you're never too old to be afraid.
- (After hearing about Kevin's experience in the basement) Basements are like that.
- (Smiles) Merry Christmas.
- (While taking Kevin off the hook) Come on. Let's get you home.
- In the novelization for Home Alone, Marley says to Kevin, “You don’t have to be so scared of me. All that stuff you hear about me - none of it’s true. Just the product of someone’s overactive imagination”.