Sumner Redstone has stepped down from his position as executive chairman of the CBS board of directors.
He will be replaced by CBS’s president and chief executive Leslie Moonves.
There is now speculation that Mr Redstone will also step down as chairman of Viacom, which owns MTV, Nickelodeon and other media assets.
Mr Redstone, who is 92 years of age, has been facing questions and legal action around his ability to lead the companies.
Last year, Mr Redstone’s former partner Manuela Herzer filed a lawsuit alleging he was mentally incapable of making decisions.
As part of that legal battle, last week Mr Redstone underwent a mental examination. The results of that test are yet to be made public.
Mr Redstone owns an 80% voting stake in CBS and its sister company Viacom.
His replacement at CBS, Mr Moonves, has served as president and chief executive of the firm since 2006, when it was split off from Viacom. He was widely seen as the successor.
Mr Redstone will become chairman emeritus of CBS and will continue to serve as the executive chairman of Viacom.
His daughter Shari Redstone will continue to serve on CBS’s board.