George Holly is the American horse buyer who comes to respect Sean and wants to take him back to America with him. He tells Sean, "It's strange how I've come to feel friendship with someone so different from myself" (43.7). It's not that strange. George Holly is basically Benjamin Malvern minus the condescension and borderline indentured servitude he forces Sean into. As Sean and Malvern have a lot in common, so do Sean and Holly. Except for Holly's tendency to wear white shoes after Labor Day. Sean wouldn't do that, if only because he wouldn't want to get blood on them.
It's interesting that George shares the same last name with the type of berry that is deadly to the capaill uisce, almost making us believe that he has some sort of trick up his sleeve. But he doesn't. Aside from being the foil to Mr. Malvern, he barely impacts the story at all. Should Sean have just gone with him to America?