Back when Sumner Redstone was a spry 85-year-old, he was asked how long he planned to continue working at Viacom and CBS. “I have no intention of ever retiring, or of dying,” was his emphatic, if optimistic, reply. Seven years later, age has sadly caught up with Mr Redstone, who no longer has an executive role at the two media groups he still controls. At Viacom, a carefully laid succession plan has unravelled: former advisers and confidants have been cast aside by Mr Redstone, who is housebound, while his daughter, Shari, has been accused by the Viacom board of manipulating her infirm father. A battle for management roles has made its way to the courts — and become very, very nasty. Some companies have handled it better than others. At Comcast, the US cable group that owns NBCUniversal, Ralph Roberts, its late founder, groomed his son, Brian to take over. Mr Roberts junior started at the bottom, working in sales, marketing and even “climbing poles” to install cable systems. When he succeeded his father in 1990, Comcast was generating annual revenues of $657m. It has since grown to become the world’s largest cable group with revenues close to $75bn last year.