Noble. In 1529, Sinclair succeeded his father, John the 3rd Earl, who had died during the Battle of Somersdale - an internecine feud between the Caithness Sinclairs and the Orkney Sinclairs.
George built the Castle of Mey overlooking the Pentland Firth between 1566 and 1572, then called Barrogil. In 1567, he was also chair of the jury who, most probably wrongly, acquitted James Hepburn, the 4th Earl of Bothwell (1536-78), third husband of Mary, Queen of Scots (1542-87), of the murder of Henry Stuart, Lord Darnley (1545-67), her second husband.
He died in Edinburgh and lies buried at Rosslyn Chapel. He was succeeded by his grandson, known as the "Wicked Earl George".