A ministerial officer within the government of the United Kingdom who performs the following functions.
1. Presides as Speaker of the House of Lords; his seat in the Chamber being known as the Woolsack. However unlike the Speaker of the House of Commons,
2. Is a member of the British Cabinet and presides over the Lord Chancellor's Department that is responsible for the administration of the court system.
3. Presides over the House of Lords in its capacity as a court.
An historical note
The office of the Lord Chancellor is also the oldest surviving British ministerial office, the origins of which date back to the tenth and eleventh centuries, when the Lord Chancellor seems to have operated as a secretary to the Court and the holder of the Great Seal of England. The role later developed and the Lord Chancellor became the the monarch's representative in the House of Lords which, prior to the developments of the eighteenth century was the most important of the two Houses of Parliament and effectively made the Lord Chancellor the leader of the King's government. (Or indeed where appropriate, the Queen's.)
Sourced from the National Digital Archive of Datasets at http://ndad.ulcc.ac.uk/datasets/AH/lordchan.htm and the The Lord Chancellor's Department online at http://www.lcd.gov.uk/lcdhome.htm