Which actress played the character of O'Brien?

Siobhan Finneran played O’Brien in Downton Abbey. Her character, Sarah O’Brien, was Lady Grantham’s lady’s maid and one of the household’s most calculating servants.

O’Brien served at Downton from the beginning of the series and used her close position to Cora Crawley to influence decisions and protect her own interests. Her most infamous act was leaving a bar of soap on the bathroom floor, contributing to Cora’s miscarriage after Cora slipped on it.

Finneran appeared as O’Brien throughout series 1–3, totaling 25 episodes. The character left Downton early in series 4 to become Lady Flintshire’s lady’s maid, later moving to India to serve the wife of the governor of the Bombay Presidency.

A common mix-up is confusing the actress with the character: Sarah O’Brien is the fictional maid, while Siobhan Finneran is the actor who portrayed her. Finneran later became widely known for roles in Happy Valley and Benidorm.