Mr. Marley was an elderly gentleman and neighbor of Kevin McCallister and his family. Somewhat stern and reclusive in demeanor, he was the subject of neighborhood gossip, which included accusations that he was in fact a murderer who had only escaped conviction because the authorities couldn't find the bodies of his victims as evidence against him. He was known for walking up and down the sidewalks of the neighborhood in wintertime, carrying a snow shovel and a bin full of salt to help clear the walks. Kevin, after seeing him at this task one night while his brother Buzz shared an account of Marley's alleged misdeeds, developed a terror of the elderly man.
Marley and Kevin had a few close encounters during the time in which Kevin was left home alone, which usually resulted in Kevin fleeing from his intimidating neighbor. However, when Kevin stopped in at a local church on Christmas Eve, having heard the choir practicing inside, he was surprised to see Marley as the only other visitor there. Marley walked up to his young neighbor and greeted him kindly, then asked Kevin's permission to sit down next to him. The two exchanged a few pleasantries, with Marley assuring Kevin that all the rumors about him were false.
The conversation between the pair turned surprisingly deep for new acquaintances, and Marley admitted to Kevin that he had come to the practice so as to hear his granddaughter, a member of the choir, sing before the performance later that night. As he further explained, he and his son had gotten into a major argument some years previously, which had ended in both of them saying they never wanted to see each other again. Kevin, baffled by this, encouraged Marley to reach out to his son and attempt reconciliation, noting that the worst that could happen would be that the situation between them wouldn't change. Kevin then left to prepare his home against the invasion of two burglars.
Having left the church himself some time later, Marley apparently observed Kevin fleeing from the home invaders and into an empty neighbors' house, where the pair cornered him. Marley stealthily crept into the house behind the two criminals, and knocked them each unconscious with a blow from his snow shovel, before seeing Kevin safely home again. The criminals were soon taken into custody by the police. The following day, Kevin looked out the window and observed Marley welcoming his son, daughter-in-law, and granddaughter warmly to his home, with Marley spotting Kevin and waving to him in the midst of the happy reconciliation.