There are plenty of unlikable characters in this dystopic nightmarescape, but we have a special reserve of hatred for Aunt Lydia. A lot of that comes from the fact that she's a woman... and yet seems totally happy to be an agent of a Republic that is organized around the systematic repression of all women. Who does that, Aunt Lydia? Ugh, we hate you.
Sometimes Aunt Lydia seems to be the voice of the Women's Center and the voice of the Republic of Gilead. It's her voice the narrator hears over and over explaining the rules and consequences of this new lifestyle. Her words shape the manipulation and brainwashing at the Center, lead the women in remaking themselves as Handmaids, and twist Biblical passages to provide justification for this new lifestyle.
One of the narrator's key observations about Aunt Lydia is this: "Aunt Lydia thought she was very good at feeling for other people" (8.27). This says a lot both about Aunt Lydia and the way the narrator sees her. Aunt Lydia believes one of her strengths is "feeling for other people," but from where we're standing (via the narrator's vantage point) this is hardly true. The only people Aunt Lydia seems to feel for are Commanders' Wives. She tries to manipulate the Handmaids into feeling compassion for the Wives:
Try to think of it from their point of view she said, her hands clasped and wrung together, her nervous pleading smile. It isn't easy for them. (3.18)
This statement reveals Aunt Lydia's qualities as a master manipulator. She "pleads" with the Handmaids, using body language like "clasped and wrung" hands to signify entreaty, while "smil[ing]" at them and seeming to act "nervous." Yet are we supposed to find any of her rhetoric legit?
At one point the narrator claims that Aunt Lydia frequently says "men are sex machines" (24.9). Then she amends this:
Aunt Lydia did not actually say this but it was implicit in everything she did say. It hovered over her head, like the golden mottoes over the saints, of the darker ages. Like them too, she was angular and without flesh. (24.10)
This is one of the narrator's more descriptive moments: we get the idea of men as sex machines floating around Aunt Lydia's head like a little thought bubble, as though she were a character in a comic strip. Perhaps Aunt Lydia's slim, ascetic body that's "angular and without flesh" makes it easier for her to encourage the Handmaids to deny their own desires and to preach about the nonsexual conception rituals so essential to the Republic of Gilead.
We hear Aunt Lydia's voice frequently throughout the book, but we only meet her once outside the narrator's flashbacks. Ironically, for someone who preaches sexual disinterest and encourages an absence of eroticism, Aunt Lydia shows up at the "climax" of the book: the women's Salvaging. She presides over the scene, which involves multiple forms of execution, with the air of a high school principal at a school assembly. At this point, though, the narrator is listening to her less and less: in person, Aunt Lydia's voice doesn't echo the way it does in her memory. The narrator already knows everything Aunt Lydia has to say.