Mellody Hobson, longtime president of Ariel Investments, is being promoted to co-CEO with founder John Rogers Jr., the company announced Thursday.

Rogers said in a letter to clients that he is selling her stock to make her the money manager’s largest shareholder. He also said he will remain chairman of Ariel and intends to manage its stock portfolios for at least another decade.

“Both her promotion as well as this share purchase represent a long-planned generational transition of leadership and ownership while simultaneously allowing us to maintain continuity,” Rogers wrote. “As many know, I have never been a seller of my Ariel stock, and these are the only shares that I ever plan to sell. I am happily doing so to level the playing field.”

Rogers said that with the sale, representing about 14% of his holdings, Hobson will own 39.5% of the firm and he will retain 34.1%. He said Ariel employees and board members own 21.8%, with the remaining 4.6% held by a small number of outsiders.

“Ariel has been my home for nearly three decades, and I am excited about the profound possibilities for the next chapter of our storied history,” Hobson said in the statement.

The wife of filmmaker George Lucas, Hobson is chairwoman of DreamWorks Animation, vice chairwoman of Starbucks and a director of JPMorgan Chase. Mayor Lori Lightfoot has named her vice chair of World Business Chicago, a public-private agency that promotes job growth.

Hobson has been president of Ariel since 2000.

In his letter to clients, Rogers said, “I have seen Mellody’s fortitude and resolve in the tensest of situations. She stands firm when others are shaky. She is a beacon in a storm —disciplined and thoughtful when others lose perspective.

“I have personally leaned on Mellody in some of the most critical times of my life, and she has been the most devoted friend and colleague that a person could have. Mellody’s loyalty has never been blind but focuses on helping others see more clearly.”