General Sir Brent Spencer was an Anglo-Irish officer in the British Army, seeing active service during the American Revolutionary War and the French Revolutionary Wars. During the Peninsular War he became General Wellesley's second-in-command on two occasions. He fought at Vimeiro and testified in Wellesley's favour at the inquiry following the Convention of Cintra. He led a division at Bussaco and two divisions at Fuentes de Onoro. After the latter action, he had an independent command in northern Portugal. Wellesley, now Lord Wellington, was not satisfied that Spencer was up to the responsibilities of second-in-command and he was replaced by Thomas Graham. Miffed, Spencer left Portugal and never returned. He became a full general in 1825.

The Battle of Buçaco or Bussaco, fought on 27 September 1810 during the Peninsular War in the Portuguese mountain range of Serra do Buçaco, resulted in the defeat of French forces by Lord Wellington's Anglo-Portuguese Army.