Blackie O'Reilly, played by Victoria Catlin, is the madame of One-Eyed Jack's, the casino/brothel just north of the Canadian border. Known as "The Black Rose", she runs Jack's at the behest of its secret owner, Benjamin Horne. In keeping with the "upscale" theme of the establishment, Blackie adorns herself in glamorous black evening gowns and exudes an air of sophistication and being a member of the "upper class." She is the highest authority at Jack's, aside from Ben Horne, eliciting absolute obedience from the cadre of prostitutes in her stable. Whenever a new girl is hired, she oversees a coin-tossing ceremony between Ben and Jerry Horne to see which man will "break her in."

Blackie is a heroin addict; sometime prior to the beginning of the series, she was the mistress of Ben Horne, who intentionally got her addicted to the drug as a means of controlling her. Blackie resents Ben's control over her, and when Ben's daughter Audrey infiltrates Jack's to try to collect information on Laura Palmer, Blackie injects her with the drug to seek vengeance on Horne. This proves to be the first step in a war between Horne and Blackie and her drug baron brother-in-law, Jean Renault, who seizes control of One-Eyed Jack's in a hostile takeover. Ultimately, Jean stabs Blackie to death, wanting to eliminate any potential competition he might have in the operation of his new business venture.