The Lord Chamberlain or Lord Chamberlain of the Household is one of the chief officers of the Royal Household in the United Kingdom and is to be distinguished from the Lord Great Chamberlain, one of the Great Officers of State.
The Lord Chamberlain is always sworn of the Privy Council, is usually a peer and before 1782 the post was of Cabinet rank. Until 1924, the position was a political one. The Lord Chamberlain is the chief functionary of the court and is generally responsible for organising all court functions. He is considered the "senior official" of the Royal Household.
The office dates from the Middle Ages, when the King’s Chamberlain often acted as the King's spokesman in Council and Parliament.
More information on the Wikipedia page [1].