Role in the film
In the town of Rathcullen, Tom Kerrigan is first seen listening to one of his friends, Darby O'Gill's stories about the leprechaun king, King Brian and the leprechauns, referred to as "little people," at his pub, the "Rathcullen Arms" along with Paddy Scanlon and his employee, Molly Malloy the barmaid.
When Pony Sugrue, the town's bully and mailman, and his two other friends mock Darby's latest story, Tom gets upset and comes to Darby's defense. He finally has the courage to confront Pony and allow him to have a glass of stout rather than whiskey if he cares to be sociable for once otherwise, he will have Father Murphy forbid him to come here at all. After Pony cooperates, Tom returns to his table to continue listening to Darby's story about his first encounter with King Brian.
After hearing the story of how King Brian also tricked Darby into making a fourth wish about a crock of gold for each of his good friends, which cost him his three wishes; especially his last one concerning his own crock of gold, Tom Kerrigan feels sad for Darby, wishing he had his own crock of gold that would make him "as rich as King Midas."
After Paddy lets out some superstitious beliefs about Darby meddling with a 5,000 year old leprechaun like King Brian that will lead to King Brian putting the come-hither on him and refusing to accept his share of the gold, Tom, Molly, and everyone else laugh at Darby's joke about leaving Paddy's share of the gold to the Church without letting Father Murphy know where he got it until everyone notices Father Murphy, who is laughing as well, in the pub and stop. Not offended and quite the understanding man with a little sense of humor himself, Father Murphy simply proceeds to announce the good news to everyone about their new bell finally arriving to them.
Tom, Molly, Paddy, and everyone else are happy to learn that Darby will bring back the bell first thing in the morning in exchange for its music as a reward for his good deed. Then, Tom watches Darby being dragged away from the pub by his daughter, Katie O'Gill for an urgent matter involving Lord Fitzpatrick's return.
The next morning, Tom, Molly, Paddy, and everyone else are happy with Darby's return with their new church bell. At the pub, everyone drinks to Darby's success until they notice something moving in Darby's sack. Amazed and shocked at the same time, Darby reveals that he has captured King Brian himself single-handedly in that sack. After Pony and his friends mock Darby again and leave, Darby offers the leprechaun a drink in front of everyone; much to their shock and amazement as they hear King Brian's gulping. After Darby leaves with King Brian in his sack, Tom is amazed to have seen the event with his own two eyes but not believe it. Then, Molly asks him to give her the glass King Brian drank in to keep it on the shelf as a souvenir and reminder of such an event and as proof of the leprechaun's existence in case of any doubts.
The next day, at the pub, Tom and everyone else watch Darby try to make his third wish. Tom tells Darby that he would wish for "a grand, big house on top of a hill as big as the castle at Cong," but Darby states the obvious that he would be but "the poorest church mouse with a house as big as a church in his hands to live in since he didn't wish for the servants to look after the house or the money to run it;" a statement that impresses Molly and Paddy, thinking he's got his head in his shoulders like Aristotle. But the wish is interrupted when Katie barges in, trying to tell him that they have to move out of their home today before Lord Fitzpatrick's return after she finds out the truth about Michael MacBride, a man whom Lord Fitzpatrick hired to replace Darby as his caretaker two weeks ago and whom Katie had just started having romantic feelings for before learning the truth about him. When Katie throws the sack with King Brian in it since her father isn't listening to her, Tom and everyone else watch in distress as Darby chases after King Brian in rabbit form while two of Pony's friends still continue mocking him.
The next morning, at the pub, Tom listens to Darby's story about how he was the only man alive today to have rode in the cóiste-bodhar (the Death Coach) last night and to have returned to tell it until Pony mocks his story for the last time. This mockery causes Tom Kerrigan to confront Pony for the last time; asking him to leave them alone since he heard that Pony was going to live in Cahersiveen. Not offended, Pony agrees; simply stating he's "heard enough silly blather about little people to last him a lifetime." Then, Michael comes in, confronts him, and a fight ensues between the two men. Finally, Michael gets his just revenge for Pony's attempt to steal his job. Tom, Molly, Paddy, and everyone else watch Pony admonish his selfish, meddlesome mother, Sheelah when she comes in to tend and baby him as he regains consciousness while Darby and Michael leave to get back to work.