English leader of the Norfolk rising of 1549, which was afterwards known as Ket's Rebellion. He was either a tanner or, more probably, a small landowner.

The rising seems to have originated in a quarrel between the people of Wymondham, in Norfolk, and a certain Flowerdew and was at first intended only as a demonstration against enclosures of common land. A feast held at Wymondham in July 1549 developed into a riot and gave the signal for the outbreak. Leading his followers to Norwich, Ket formed a camp on Mousehold Heath, where he is said to have commanded 16,000 men, introduced a regular system of discipline and justice, and blockaded the city. He refused the royal offer of an amnesty on the ground that innocent and just men had no need of pardon and, on Aug. 1, 1549, attacked and took possession of Norwich. But the rebels were soon driven out by forces under John Dudley, earl of Warwick (Northumberland, John Dudley, duke of, earl of Warwick, Viscount Lisle, Baron Lisle), who attacked their main body at Dussindale on August 27. Ket's men were easily routed by the trained soldiery, and Robert Ket and his brother William were seized and taken to London, where they were condemned to death for treason. Both were executed early in December 1549, Robert at Norwich and William at Wymondham.