Goldman Sachs Group Inc. /zigman2/quotes/209237603/composite GS -1.20% disclosed an ownership stake of about 20.95 million shares or 18.5% of marketing services company Stagwell Inc. /zigman2/quotes/208009087/composite STGW -0.29% , according to filings on Wednesday. The holding is valued at about $210 million based on Stagwell's stock price of $10.05 a share on Thursday. Stagwell announced on Sept. 23 that it would convert Series 6 and Series 8 preferred stock as part of an effort to streamline and simplify its capital structure, but it did not name the entity receiving the stock. A spokesperson for the company said Goldman had held the convertible stock as part of a prior investment in the company. Mark Penn, the ex-Microsoft Corp. /zigman2/quotes/207732364/composite MSFT -1.85% executive known for popularizing the term "soccer mom," founded Stagwell in 2015 to invest in advertising, research, data analytics, public relations and online marketing companies. The firm raised $250 million in funding and drew in loans and other financing, including backing from Microsoft co-founder Steve Ballmer.