District of Columbia Attorney General Karl Racine on Wednesday said he has added embattled Facebook Inc. /zigman2/quotes/205064656/composite FB -0.07% Chief Executive Mark Zuckerberg as defendant in a 2018 lawsuit related to Cambridge Analytica and Facebook's failure to protect user data. Racine is the first regulator to attempt to hold the company's co-founder personally responsible. "Allowing third-party apps like Cambridge Analytica to access user data was Mark Zuckerberg's brainchild," Racine tweeted. "Adding him to our lawsuit is unquestionably warranted and should send a message that corporate leaders will be held accountable for their actions." A Facebook spokesperson called the allegations "as meritless today as they were more than three years ago, when the District filed its complaint. We will continue to defend ourselves vigorously and focus on the facts." Facebook shares are flat in early-afternoon trading Wednesday. For they year, they are up 25%. The broader S&P 500 index /zigman2/quotes/210599714/realtime SPX +1.42% is up 21% in 2021.