Sarah O'Brien is a character and one of the two primary villains on the long-running drama series, Downton Abbey. She was played for the series first three seasons by actress Siobhan Finneran.
Duplicitous lady's maid
Sarah O'Brien, known as Miss O'Brien below stairs, and as simply O'Brien upstairs, was the first lady's maid of the Countess of Grantham. She was one of the most scheming members of the servants staff. She and Thomas Barrow, one of the footman, were partners in scheming for the first two seasons.
They were most notably seen, usually in the courtyard near the servant's entrance, where they would scheme their next devious moves, and smoke. Notably, Sarah (and a later character, Laura Edmunds) would be one of the few women who smoked cigarettes, which was often frowned upon at that time.
O'Brien's position wasn't always secure. Due to her tendency to gossip when she wasn't supposed to, her position was usually under fire. She would tend to not follow orders, especially given by Mrs. Hughes, her superior.
In the first season, she and Thomas would do everything in their power to undermine and derail John Bates in his new job as valet. In fact, in the first episode, she deliberately kicked Bates' walking stick out from underneath him causing him to fall down in the gravel.
After that, she and Thomas also tried to have him sacked for theft, when she and Thomas stole a snuff box that belonged to the Earl of Grantham and hid it in Bates' room. However, Bates and the head housemaid, Anna Smith, turned the tables on the two of them and hid the snuff box in O'Brien's room! She had been caught by Mrs. Hughes turning her room inside out!
In the first season finale, O'Brien had left a piece of soap near Cora's tub, causing her to slip and miscarry her late in life pregnancy. This was due to a misunderstanding in which she thought she was going to be sacked, but in reality, Cora was actually looking for a lady's maid for the Dowager Countess of Grantham, Violet Crawley.
In the second season, O'Brien had felt so guilty over what she had done to her lady, that she was overly protective of Cora. So devoted was she to Cora that she never left her side, especially when the Spanish flu ravaged her.
In the third season, things had changed for her and Thomas. For many and varied reasons, the two had a falling out, and they were no longer friends, but bitter enemies. They would do everything possible to undermine the other. Much of the venom that came from Thomas had to do with O'Brien's nephew, Alfred Nugent, coming on as a footman. Thomas was jealous of the new footman.
O'Brien would take Robert Crawley's evening shirts, hoping that Thomas would be sacked from the role of valet. However, visiting lady's maid, Miss Reed, the maid to Martha Levinson, would catch her at the act, but would help Alfred to find them and bring them back to the Earl. O'Brien would later confront him, by yelling that he was not doing his job. She would later compare him to Tom Mix making threats and ordered him to get Robert's pajamas ready!
O'Brien nearly had Thomas arrested after she manufactured things to where he had a one-sided attraction towards a new footman named James Kent. Alfred had caught Thomas kissing him, and both Jimmy and Alfred demanded he be sacked without a reference, but the Earl of Grantham and Charles Carson, the butler, convinced the two of them not to do so.
In the first episode of the Fourth Season, O'Brien had left the Crawley's employ and became the new lady's maid to Susan MacClare, the niece of Violet Crawley, after she and her former lady's maid, Wilkins, had a falling out.
O'Brien would be replaced by Edna Braithwaite, who was no better (she connived to marry Tom Branson through deceit and was sacked for it); and then by Phyllis Baxter, who was, by far, a vast improvement to both of them.