In 1249, Henry III granted the castle to his brother-in-law, Simon de Montfort, for life. But in 1264 de Montfort rebelled against the King, and was killed in battle. His son retreated to Kenilworth. The King's son, Edward, arrived in the spring of 1266, and a great siege was underway. It ended eight months later when de Montfort was allowed to go into exile. Other famous men who occupied Kenilworth included Roger Morimer, John of Gaunt and Robert Dudley.
If you would like more information on the Kenilworth Castle, check out this 1835 article from the Penny Magazine.