Both Mr. Charrington and O'Brien are members of the Party, both are intelligent and knowledgeable, and both deceive Winston and Julia.
Both men present as benign. Mr. Charrington, though in reality much younger, presents himself as a harmless and humble 63-year-old shopkeeper in a velvet jacket. He pretends to be a prole with a Cockney accent. O'Brien has a blunt, pleasant look in his black overalls and pretends to be part of the underground Winston is seeking.
Both men supply Winston, insatiably searching for knowledge, with information he craves. Mr. Charrington recites to Winston part of the "oranges and lemons" rhyme and even explains some of the history and the background of the verses. O'Brien invites Winston and Julia to his apartment, offers them wine and give Winston "The Book," supposedly written by Goldstein, that explains oligarchic collectivism. Both men thus win Winston's (and Julia's) trust while betraying them.
Both Mr. Charrington, a member of the Thought Police, and O'Brien are ruthless men dedicated to the Party. They know how to manipulate others. Both are frightening because they are able to fake being humane and benevolent so successfully. What is most troubling about both men is that they clearly have the knowledge, personality and intelligence to make other choices and yet have chosen a dehumanizing path.